Geominerals/Hydroxides

Hydroxide minerals generally contain more than 25 molecular % OH. But, some classification systems include minerals as hydroxides if they are found to contain hydroxides.

The hydroxide ion is a natural part of water because of the self-ionization reaction in which its complement, hydronium, is passed hydrogen:^[1]

H
₃O⁺
+ OH⁻
⇌ 2H
₂O

The equilibrium constant for this reaction, defined as

K
_w = [H⁺
][OH⁻
], where [H⁺
] denotes the concentration of hydrogen cations and [OH⁻
] the concentration of hydroxide ions.

has a value close to 10⁻¹⁴ at 25 °C, so the concentration of hydroxide ions in pure water is close to 10⁻⁷ mol∙dm⁻³, in order to satisfy the equal charge constraint. The pH of a solution is equal to the decimal cologarithm of the hydrogen cation concentration; strictly speaking pH is the cologarithm of the hydrogen cation. The pH of pure water is close to 7 at ambient temperatures. The concentration of hydroxide ions can be expressed in terms of pOH, which is close to (14 − pH), pOH signifies the minus the logarithm to base 10 of [OH⁻
], alternatively the logarithm of 1/[OH⁻
], so the pOH of pure water is also close to 7. Addition of a base to water will reduce the hydrogen cation concentration and therefore increase the hydroxide ion concentration (increase pH, decrease pOH) even if the base does not itself contain hydroxide. For example, ammonia solutions have a pH greater than 7 due to the reaction NH₃ + H⁺ ⇌ NH⁺
₄, which decreases the hydrogen cation concentration, which increases the hydroxide ion concentration. pOH can be kept at a nearly constant value with various buffer solutions.

In aqueous solution^[2] the hydroxide ion is a base in the Brønsted–Lowry sense as it can accept a proton, in this context proton is the term used for a solvated hydrogen cation, from a Brønsted–Lowry acid to form a water molecule. It can also act as a Lewis base by donating a pair of electrons to a Lewis acid. In aqueous solution both hydrogen and hydroxide ions are strongly solvated, with hydrogen bonds between oxygen and hydrogen atoms. Indeed, the bihydroxide ion H
₃O⁻
₂ has been characterized in the solid state. This compound is centrosymmetric and has a very short hydrogen bond (114.5 pm) that is similar to the length in the bifluoride ion HF⁻
₂ (114 pm).^[3] In aqueous solution the hydroxide ion forms strong hydrogen bonds with water molecules. A consequence of this is that concentrated solutions of sodium hydroxide have high viscosity due to the formation of an extended network of hydrogen bonds as in hydrogen fluoride solutions.

In solution, exposed to air, the hydroxide ion reacts rapidly with atmospheric carbon dioxide, acting as an acid, to form, initially, the bicarbonate ion.

OH⁻ + CO₂ ⇌ HCO⁻
₃

The equilibrium constant for this reaction can be specified either as a reaction with dissolved carbon dioxide or as a reaction with carbon dioxide gas (see carbonic acid for values and details). At neutral or acid pH, the reaction is slow, but is catalyzed by the enzyme carbonic anhydrase, which effectively creates hydroxide ions at the active site.

Solutions containing the hydroxide ion attack glass. In this case, the silicates in glass are acting as acids. Basic hydroxides, whether solids or in solution, are stored in airtight plastic containers.

The hydroxide ion can function as a typical electron-pair donor ligand, forming such complexes as tetrahydroxidoaluminate [Al(OH)₄]⁻. It is also often found in mixed-ligand complexes of the type [ML_x(OH)_y]^z+, where L is a ligand. The hydroxide ion often serves as a bridging ligand, donating one pair of electrons to each of the atoms being bridged. As illustrated by [Pb₂(OH)]³⁺, metal hydroxides are often written in a simplified format. It can even act as a 3-electron-pair donor, as in the tetramer [PtMe₃(OH)]₄.^[4]

When bound to a strongly electron-withdrawing metal centre, hydroxide ligands tend to ionise into oxide ligands. For example, the bichromate ion [HCrO₄]⁻ dissociates according to

[O₃CrO–H]⁻ ⇌ [CrO₄]²⁻ + H⁺

with a pK_a of about 5.9.^[5]

Abhurite (IMA symbol: Abh^[6]) is a mineral of tin, oxygen, hydrogen, and chlorine with the formula Sn
₂₁O
₆(OH)
₁₄Cl
₁₆^[7][8] or Sn
₃O(OH)
₂Cl
₂.^[9] It is named after its type locality, a shipwreck with tin ingots at Sharm Abhur, a cove near Jeddah in the Red Sea. Abhurite forms alongside other tin minerals like romarchite and cassiterite.^[10]

Abhurite formed on tin materials when in contact with sea water. The mineral was described in 1977 from a shipwreck near Hidra Island, Norway, where it occurred on pewter plates. However, that report was not recognized by the IMA, International Mineralogical Association.^[8] Along with Sharm Abhur and the shipwreck near Hidra Island, abhurite was found on tin ingots in the Uluburun shipwreck. On the ingots, it was found with other tin minerals like cassiterite and romarchite, and calcium carbonate minerals like calcite and aragonite.^[11]

Actinolite (IMA symbol Act^[6]) has the chemical formula Ca
₂(Mg²⁺
_4.5-2.5Fe²⁺
_0.5-2.5)Si
₈O
₂₂(OH)
₂, is an amphibole silicate mineral. The name actinolite is derived from the Greek word aktis (ἀκτίς), meaning "beam" or "ray", because of the mineral's fibrous nature.^[12]. Actinolite is an intermediate member in a solid-solution series between magnesium-rich tremolite, Ca
₂(Mg²⁺
_5.0-4.5Fe²⁺
_0.0-0.5)Si
₈O
₂₂(OH)
₂, and iron-rich ferro-actinolite, ☐Ca
₂(Mg²⁺
_2.5-0.0Fe²⁺
_2.5-5.0)Si
₈O
₂₂(OH)
₂. Mg and Fe ions can be freely exchanged in the crystal structure. Like tremolite, asbestiform actinolite is regulated as asbestos.

Actinolite is commonly found in metamorphic rocks, such as contact aureoles surrounding cooled intrusive igneous rocks. It also occurs as a product of metamorphism of magnesium-rich limestones.

The old mineral name uralite is at times applied to an alteration product of primary pyroxene by a mixture composed largely of actinolite. The metamorphosed gabbro or diabase rock bodies, referred to as epidiorite, contain a considerable amount of this uralitic alteration.

Acuminite (IMA symbol: Acu^[6]) is a rare halide mineral of with chemical formula: SrAlF
₄(OH)·(H
₂O). Its name comes from the Latin word acumen, meaning "spear point". Its Mohs scale of mineral hardness rating is 3.5.

Acumenite has only been described from its type locality of the cryolite deposit in Ivigtut, Greenland.^[13]

Adamite (IMA symbol: Ad^[6]) is a zinc arsenate hydroxide mineral, has the chemical formula Zn
₂AsO
₄OH, and is a mineral that typically occurs in the oxidized or weathered zone above zinc ore occurrences.

Adamite occurs as a secondary mineral in the oxidized zone of zinc- and arsenic-bearing hydrothermal mineral deposits. It occurs in association with smithsonite, hemimorphite, scorodite, olivenite, calcite, quartz and iron and manganese oxides.^[14]

The rare mineral adelite, (IMA symbol Ade^[6]) is a calcium, magnesium, arsenate with the chemical formula CaMgAsO
₄OH, forming a solid solution series with the vanadium-bearing mineral gottlobite, where various transition metals substitute for magnesium and lead replaces calcium leading to a variety of similar minerals in the adelite - duftite group.

Aeschynite has the chemical formula (Ce,Ca,Fe,Th)(Ti,Nb)
₂(O,OH)
₆.^[15]

Here there are two oxygen groups:

1. O, oxygenides, from 11.1 to 55.6 at % likely, and
2. OH, hydroxides, from 55.6 to 11.1 at % likely.

The IMA symbol is Aes-Ce.^[6]

Chemical formula: (Ce,Ca,Fe,Th)(Ti,Nb)
₂(O,OH)
₆.

The "-(Ce)" means it has more cerium than the yttrium variety aeschynite-(Y). Its Mohs scale rating is 5–6.

Aeschynite-(Nd) is a rare earth mineral of neodymium, cerium, calcium, thorium, titanium, niobium, oxygen, and hydrogen with formula: (Nd,Ce,Ca,Th)(Ti,Nb)
₂(O,OH)
₆. Its name comes from the Greek word for "shame". Its Mohs scale rating is 5 to 6. It is a member of the hydroxide minerals.

It was first reported for an occurrence in Bayan Obo Inner Mongolia in 1982. In that rare earth mining deposit it occurs in veins within metamorphosed dolomite and slate. It occurs associated with aegirine, riebeckite, barite, fluorite, albite, phlogopite and magnetite.^[16] The IMA symbol is Aes-Nd.^[6]

Aeschynite-(Y) (or Aeschinite-(Y), Aeschynite-(Yt), Blomstrandine, Priorite) is a rare earth mineral of yttrium, calcium, iron, thorium, titanium, niobium, oxygen, and hydrogen with formula: (Y,Ca,Fe,Th)(Ti,Nb)
₂(O,OH)
₆. Its name comes from the Greek word for "shame". Its Mohs scale rating is 5 to 6. The IMA symbol is Aes-Y.^[6]

The chemical formula is Ca
₃(SiO
₃OH)
₂·2H
₂O. Afwillite (IMA symbol: Afw^[6]) is a calcium hydroxide nesosilicate mineral that occurs as glassy, colorless to white prismatic monoclinic crystals, has a Mohs scale hardness between 3 and 4, occurs as an alteration mineral in contact metamorphism of limestone,^[17] in association with apophyllite, natrolite, thaumasite, merwinite, spurrite, gehlenite, ettringite, portlandite, hillebrandite, foshagite, brucite and calcite.^[17]

It was first described in 1925 for an occurrence in the Dutoitspan Mine, Kimberley, South Africa and was named for Alpheus Fuller Williams (1874–1953), a past official of the De Beers diamond company.^[18]

Afwillite has had a couple of formulas:

1. Ca
   ₃Si
   ₂O
   ₄(OH)
   ₆,^[15] and
2. Ca
   ₃(HSiO
   ₄)
   ₂·2H
   ₂O.^[19]

Afwillite may form in fractured veins of the mineral spurrite. Jennite, afwillite, oyelite and calcite are all minerals that form in layers within spurrite veins. Afwillite, and calcite, may form from precipitated fluids. Jennite is actually an alteration of afwillite, but both formed from calcium silicates through hydration. Laboratory studies determined that afwillite forms at a temperature below 200 °C (392 °F), usually around 100 °C.^[20] Afwillite and spurrite are formed through contact metamorphism of limestone.^[21] Contact metamorphism is caused by the interaction of rock with heat and/or fluids from a nearby crystallizing silicate magma.^[22]

Structurally, afwillite is a nesosilicate with isolated SiO₄ tetrahedra.

Afwillite has two oxides:

1. 2SiO₄, Silicates, and
2. 2H₂O, oxidanes, with each having about 50 molecular %.

Calcium does not occur as native calcium. Here it links to the oxygens in the silicate tetrahedra and the oxidanes. Afwillite is 47.6 at % silicate and 28.6 at % oxidane.

Afwillite has a complex monoclinic structure, and the silicon tetrahedra in the crystal structure are held together by hydrogen bonds.^[23] It has perfect cleavage]] parallel to its (101) and poor cleavage parallel to its (100) faces.^[24] It is biaxial and its 2V angle, the measurement from one optical axis to the other optical axis, is 50 – 56 degrees. When viewed under crossed polarizers in a petrographic microscope, it displays first-order orange colors, giving a maximum birefringence of 0.0167 (determined by using the Michel- Levy chart). Afwillite is optically positive. Additionally, it has a prismatic crystal habit.^[20] Under a microscope afwillite looks like wollastonite, which is in the same family as afwillite.

Afwillite is composed of double chains that consist of calcium and silicon polyhedral connected to each other by sharing corners and edges. This causes continuous sheets to form parallel to its miller index [-101] faces. The sheets are bonded together by hydrogen bonds and are all connected by Ca-Si-O bonds (Malik and Jeffery, 1976).^[23] Each calcium atom is in 6-fold octahedral coordination with the oxygen, and the silicon is in 4-fold tetrahedral coordination around the oxygen. Around each silicon there is one OH group and there are three oxygens that neighbor them.^[23] The silicon tetrahedra are arranged so that they share an edge with calcium(1), and silicon(2) shares edges with the calcium(2) and calcium(3) polyhedral.^[23] The silicon tetrahedra are held together by the OH group and hydrogen bonding occurs between the hydrogen in the OH and the silicon tetrahedra. Hydrogen bonding is caused because the positive ion, hydrogen, is attracted to negatively charge ions which, in this case, are the silicon tetrahedra.^[22]

Agradite has the chemical formula (REE,Ca)Cu
₆(AsO
₄)
₃(OH)
₆·3H
₂O, a repeating unit.

Agardite is a mineral group consisting of agardite-(Y),^[25][26] agardite-(Ce),^[27] agardite-(Nd),^[28] and agardite-(La).^[29] They have been allocated the IMA symbols Agr-Y, Agr-Ce, Agr-Nd and Agr-La.^[6] They comprise a group of minerals that are hydrous hydrated arsenates of rare-earth elements (REE) and copper, with the general chemical formula (REE,Ca)Cu
₆(AsO
₄)
₃(OH)
₆·3H
₂O. Yttrium, cerium, neodymium, lanthanum, as well as trace to minor amounts of other REEs, are present in their structure. Agardite-(Y) is probably the most often found representative. They form needle-like yellow-green (variably hued) crystals in the hexagonal crystal system. Agardite minerals are a member of the mixite structure group, which has the general chemical formula Cu²⁺
₆A(TO
₄)
₃(OH)
₆·3H
₂O, where A is a REE, Al, Ca, Pb, or Bi, and T is P or As. In addition to the four agardite minerals, the other members of the mixite mineral group are calciopetersite,^[30] goudeyite,^[31] mixite,^[32] petersite-(Ce),^[33] petersite-(Y),^[34][26] plumboagardite,^[35] and zálesíite.^[36]

Agardite-(Y) from the Bou Skour mine in Djebel Sarhro, Morocco was the first of the agardite-group minerals to be characterized.^[25] It was described by Dietrich in 1969 and was named after Jules Agard, a French geologist at the Bureau de Recherches Géologiques et Minières, Orléans, France.^[37] Agardite-group minerals have subsequently been found in Germany,^[38] Czech Republic,^[39] Greece,^[40] Italy,^[41] Japan,^[42] Namibia,^[43] Poland,^[44] Spain,^[42] Switzerland,^[45] the United Kingdom,^[46] and the United States.^[47]

Agrinierite (K
₂(Ca,Sr)(UO
₂)
₃O
₃(OH)
₂·5H
₂O)^[48] is a mineral often found in the oxidation zone of uranium deposits. The 'IMA symbol is Agn.^[6] It is named for Henry Agrinier (1928–1971), an engineer for the Commissariat à l'Énergie Atomique.

Chemical formula for Agrinierite is (K
₂,Ca,Sr)U
₃O
₁₀·4(H
₂O).^[49][50]

Formula for Agrinierite is K
₂(Ca,Sr)[(UO
₂)
₃O
₃(OH)
₂]
₂·5H
₂O.^[51]

Aheylite (International Mineralogical Association (IMA) symbol: Ahe^[6]) is a rare phosphate mineral with formula (Fe²⁺
Zn)Al
₆[(OH)
₄(PO
₄)
₂]
₂·4(H
₂O) that occurs as pale blue to pale green triclinic crystal masses,^[52] the newest member of the turquoise group in 1984 by International Mineralogical Association Commission on New Minerals and Mineral Names.

The turquoise group has a basic formula of A
_(0-1)B
₆(PO
₄)
_4−x(PO
₃OH)
_x(OH)
₈·4H
₂O. This group contains six minerals: aheylite, planerite, turquoise, faustite, chalcosiderite, and an unnamed Fe²⁺
-Fe³⁺
analogue. Aheylite is distinguished in this group by having Fe²⁺
dominant in the A-site. The ideal aheylite has a formula of Fe²⁺
Al
₆(PO
₄)
₄(OH)
₈·4H
₂O, a pale blue or green. With the turquoise family the blue color is said to come from the octahedral coordination of Cu²⁺
in the absence of Fe³⁺
.^[53]

It was first described for an occurrence in the Huanuni mine, Huanuni, Oruro Department, Bolivia, and named for Allen V. Heyl (1918–2008), an economic geologist for the United States Geological Survey.^[54] It was discovered by Eugene Foord and Joseph Taggart.^[53]

In addition to the type locality in Bolivia it has been reported from the Bali Lo prospect in the Capricorn Range, Western Australia^[52] and the Les Montmins Mine, Auvergne, France.^[54] It is a turquoise group mineral and occurs as a late hydrothermal phase in a tin deposit associated with variscite, vivianite, wavellite, cassiterite, sphalerite, pyrite and quartz in the type locality.^[52][55]

It is found as an isolated mass of hemispheres and spheres clumped together. It has a vitreous to dull luster. It has a hackly to splintery fracture and it has a brittle tenacity. The hardness is about 5-5.5, and the specific gravity is 2.84. As far as optical properties, it had thin flakes; ipale blue, green to blue-green color; it streaks white, and has a subvitreous luster.^[53]

Ajoite has the chemical formula (Na,K)Cu
₇AlSi
₉O
₂₄(OH)
₆·3H
₂O,^[56] and minor Mn, Fe and Ca are usually also present in the structure.^[57] Ajoite is used as a minor ore of copper.

Ajoite (International Mineralogical Association (IMA) symbol Aj^[6]) is a hydrated sodium potassium copper aluminium silicate hydroxide mineral.

Ajoite is a secondary mineral that forms from the oxidation of other secondary copper minerals in copper-rich base metal deposits in massive fracture coatings, in vein fillings, and in vugs. It may form from shattuckite and also it may be replaced by shattuckite.^[57]

At the type locality it is associated with shattuckite, conichalcite, quartz, muscovite and pyrite.^[58][56]

Ajoite is named after its type locality, the New Cornelia Mine in the Ajo District of Pima County, Arizona. Type specimen material is conserved at the National Museum of Natural History, Washington DC, USA, reference number 113220.

Other localities include Wickenburg and Maricopa County, Arizona, within the United States, and the Messina (Musina) District in South Africa. Quartz specimens from the defunct Messina Mines on the border between Zimbabwe and South Africa are well known for their inclusions of blue copper silicate minerals such as shattuckite, papagoite and ajoite,^[59] but ajoite from American localities does not occur like this.

Akaganeites have the chemical formula Fe³⁺
O(OH,Cl).

Akaganeite (International Mineralogical Association (IMA) symbol: Akg^[6]), also written as the deprecated Akaganéite,^[60] is a chloride-containing iron(III) oxide-hydroxide mineral, formed by the weathering of pyrrhotite (Fe
_(1−x)S).

Akaganeite is often described as the β phase of anhydrous Iron(III) oxide-hydroxide (ferric oxyhydroxide) FeOOH, but some chloride (or fluoride) ions are normally included in the structure,^[61] so a more accurate formula is FeO
_0.833(OH)
_1.167Cl
_0.167.^[62] Nickel may substitute for iron, yielding the more general formula (Fe³⁺
,Ni²⁺
)
₈(OH,O)
₁₆Cl
_1.25^[63]

Akaganeite has a metallic luster and a brownish yellow streak, crystal structure is monoclinic and similar to that of hollandite BaMn
₈O
₁₆, characterised by the presence of tunnels parallel to the c-axis of the tetragonal lattice. These tunnels are partially occupied by chloride anions that give to the crystal its structural stability.^[62]

Occurrence: The mineral was discovered in the Akagane mine in Iwate, Japan, for which it is named. It was described by the Japanese mineralogist Matsuo Nambu in 1968,^[64] but named as early as 1961.^[65][66]

Akaganeite has also been found in widely dispersed locations around the world and in rocks from the Moon that were brought back during the Apollo Project. The occurrences in meteorites and the lunar sample are thought to have been produced by interaction with Earth's atmosphere. It has been detected on Mars through orbital imaging spectroscopy.^[67]

Akrochordites have the following formulae:

1. Formula: (Mn²⁺
   ,Mg)
   ₅(AsO
   ₄)
   ₂(OH)
   ₄ · 4H
   ₂O^[68][69]
2. Chemical formula: Mn²⁺
   ₄Mg(AsO
   ₄)
   ₂(OH)
   ₄·4H
   ₂O.^[70][71]

Environment: "A rare mineral in hausmannite ore from a metamorphosed Fe-Mn orebody (Långban, Sweden); in a metamorphosed stratiform zinc orebody (Sterling Hill, New Jersey, USA)."^[71]

Akrochordite (International Mineralogical Association (IMA) symbol: Akr^[6]) is a rare hydrated arsenate mineral that represents a small group of rare manganese (Mn) arsenates and, similarly to most other Mn-bearing arsenates, possess pinkish colour, typically associated with metamorphic Mn deposits.^[72][73]

Aksaites have the formula Mg[B
₆O
₇(OH)
₆] · 2H
₂O,^[74] IMA symbol is Aks, IMA formula: MgB
₆O
₇(OH)
₆ · 2H
₂O.^[6]

Aksaite is orthorhombic.^[75]

"According to the results of the structural analysis, the largest thermal motion is shown by the water molecule, O(14), which is only linked to the Mg atom and to O(13") through a hydrogen bond. The thermal amplitude of two of the three triangular hydroxyls, O(11) and O(13), involved in a bond with boron as well as in two hydrogen bonds, is rather large. Much smaller is the displacement of the O(12) hydroxyl which is also participating to a bond with magnesium. It is also easy to understand the slight thermal motion of the water molecule O(15), which is involved in a bond with magnesium and in three hydrogen bonds as well."^[75]

Aldermanite (International Mineralogical Association (IMA) symbol: Adm^[6]) is a rare hydrated phosphate mineral with formula Mg
₅Al
₁₂(PO
₄)
₈(OH)
₂₂·32H
₂O.^[76][77][78] It's named after Arthur Richard Alderman (1901–1980), Professor of Geology and Mineralogy, University of Adelaide. Its type locality is Moculta Phosphate Quarry (Klemm's Quarry), Angaston, Barossa Valley, North Mount Lofty Ranges, Mount Lofty Ranges, South Australia, Australia.

Aliettite (International Mineralogical Association (IMA) symbol: Ali^[6]) is a complex phyllosilicate mineral of the smectite group with a formula of (Ca
_0.2Mg
₆(Si,Al)
₈O
₂₀(OH)
₄·4H
₂O)^[79] or [Mg
₃Si
₄O
₁₀(OH)
₂](Ca
_0.5,Na)
_0.33(Al,Mg,Fe²⁺
)
_2–3(Si,Al)
₄O
₁₀(OH)
₂·n(H
₂O).^[80][81]

It is a soft, colorless to pale yellow or green earthy mineral which crystallizes in the monoclinic system as minute tabular to platy crystals.^[79]

It was first described in 1968 for an occurrence in Monte Chiaro, Albareto, Parma Province, Emilia-Romagna, Italy and named for the Italian mineralogist Andrea Alietti (born 1923).^[79]

A regularly interstratified talc-saponite mineral.^[79]

Common Impurities: Mn.^[79]

Common Associates: Calcite CaCO
₃, Chlorite Group A group of mostly monoclinic (also triclinic or orthorhombic) micaceous phyllosilicate minerals with a structure consisting of T-O-T layers with two layers having their silicate tetrahedral apices pointing towards each other, separated by an interlayer that may be simple octahedrally coordinated cations or which may be a brucite-*like* layer of two sheets of closely packed OH groups with the interstices between sheets providing the octahedral coordination site; the T-O-T layers and interlayer are bonded by electrostatic and hydrogen bonding forces; as the "a" and "b" directions of the T-O-T layer may be oriented to the interlayer "a" and "b" directions in twelve different stacking sequences, resulting in twelve different polytype possibilities (not all of which have been found in Nature yet for each species), Serpentine Subgroup D
₃[Si
₂O
₅](OH)
₄, D = Mg, Fe, Ni, Mn, Al, Zn, Talc Mg
₃Si
₄O
₁₀(OH)
₂.^[79]

It occurs in serpentinized ophiolites and their residual soil. It also occurs in altered dolomite. Associated minerals include talc, chlorite, serpentine and calcite.^[81] In addition to the type locality in Italy it has been reported from Kinshasa, Katanga;^[81] the Chelyabinsk Oblast of the southern Urals and the Turii alkaline Massif of the Kola Peninsula in Russia; the Zirabulak Mountains of Uzbekistan; and the Goldstrike Mine of Eureka County, Nevada, US.^[79]

Formula: Mn²⁺
₇(AsO
₄)
₂(OH)
₈.^[82] Crystal system: Monoclinc.^[82]

Isostructural with: Argandite.^[82]

Allactite (International Mineralogical Association (IMA) symbol: Ala^[6]) is a rare arsenate mineral of metamorphosed manganese zinc ore deposits, found in Sweden and New Jersey, US, name originated from Greek αλλάκτειν (allaktein) meaning "to change", referring to the strong pleochroism of the mineral.^[83]

Allactite is the arsenate analogue of argandite and waterhouseite.^[82]

Geochemistry: In the structure there are 4 fully occupied hydrogen sites and at least 9 energetically favourable mono-, bi- and trifurcated hydrogen bonds (Gatta et al., 2016).^[82]

Geological Setting: in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA).^[82]

Associated Minerals at Type Locality: Synadelphite, Pyrochroite, Hematolite, Hausmannite and Fluorite.^[82]

Other Members of the Allactite Group: Argandite Mn
₇(VO
₄)
₂(OH)
₈, Raadeite Mg7(PO
₄)
₂(OH)
₈.^[82]

Allanpringite has the formula: Fe³⁺
₃(PO
₄)
₂(OH)
₃·5H
₂O.

Allanpringite (International Mineralogical Association (IMA) symbol: Apg^[6]) is a phosphate mineral named after Australian mineralogist Allan Pring of the South Australian Museum, an Fe³⁺
analogue Al-phosphate mineral wavellite, but it has a different crystal symmetry – monoclinic instead of orthorhombic in wavellite, forms needle-like crystals, which are always twinned and form parallel bundles up to about 2 mm long, are often found in association with other iron phosphates in abandoned iron mines.^[84][85]

Alleghanyite (International Mineralogical Association (IMA) symbol: Alh^[6]) is a moderately rare humite mineral with the formula Mn²⁺
₅(SiO
₄)
₂(OH)
₂,^[86] belonging to the nesosilicates class.^[86] In general its occurrences are related with metamorphic (metamorphosed) manganese deposits. The mineral is named after Alleghany County, North Carolina, US.^[86]

Crystal system: Monoclinic.^[86]

Member of the Manganhumite subgroup > Humite group.^[86]

Dimorph of Ribbeite.^[86]

Isostructural with Chegemite, Chondrodite, Edgrewite, Humite, Hydroxylchondrodite, Hydroxylclinohumite, Jerrygibbsite, Kumtyubeite, Leucophoenicite, Manganhumite, Norbergite, Reinhardbraunsite, Ribbeite, Sonolite.^[86]

May occur as pink to red-brown fine-grained masses or rare crystals on vein fractures.^[86]

Geological Setting: in veins crosscutting franklinite ore near pegmatites in a metamorphosed stratiform Zn-Mn deposit.^[86]

Geological Setting of Type Material: Hydrothermally deposited, in lenses in a manganese-bearing vein.^[86]

Associated Minerals at Type Locality: Spessartine, Rhodonite and Galaxite.^[86]

Althausite (International Mineralogical Association (IMA) symbol: Ahs^[6]) is a relatively simple magnesium phosphate mineral with formula Mg
₂(PO
₄)(OH,F). It is very rare. Original occurrences are magnesite deposits among serpentinites. It is named after Egon Althaus (born 1933), a mineralogist at the University of Karlsruhe, Germany.^[87][88][89]

Althupite (International Mineralogical Association (IMA) symbol: Ahp^[6]) is a rare aluminium thorium uranyl phosphate mineral, named after its composition (ALuminium, THorium, Uranium, and Phosphorus), with a complex formula written as AlTh(UO
₂)
₇(PO
₄)
₄O
₂(OH)
₅·15H
₂O, from a granitic pegmatite.^[90][91][92]

Chemical formula: Al
₂(SO
₄)(OH)
₄•7H
₂O.^[93]

Crystal system: Monoclinic.^[94]

Member of the Aluminite Group.^[94]

Other Members of this group: Mangazeite Al
₂(SO
₄)(OH)
₄·3H
₂O.^[94]

Occurrence: "Typically in clays or lignites, formed by the reaction of sulfate-bearing solutions from the decomposition of marcasite or pyrite at moderate temperatures with aluminous silicates; as a volcanic sublimate; in sulfur deposits; rarely in caves."^[93]

"Found as earthy reniform or nodular masses composed of tiny fibrous crystals."^[94]

Geological Setting: "Found as concretionary deposits in Tertiary to Quaternary clays, marls, and lignites, formed by the action of sulfate solutions derived from the decay of pyrite or marcasite on aluminous silicates. Typically in clays or lignites, formed by the reaction of sulfate-bearing solutions from the decomposition of marcasite or pyrite at moderate temperatures with aluminous silicates; as a volcanic sublimate; in sulfur deposits; rarely in caves."^[94]

Association: "Basaluminite, gibbsite, epsomite, gypsum, celestine, dolomite, goethite."^[93]

Alunite (International Mineralogical Association (IMA) symbol: Alu^[6]) is a hydroxylated aluminium potassium sulfate mineral, formula KAl
₃(SO
₄)
₂(OH)
₆.^[95]

Polymorphism & Series: Forms a series with natroalunite.^[95]

Mineral Group: Alunite group.^[95]

Alunite Group > Alunite Supergroup.^[96]

Occurrence: Formed between 15°C and 400°C by the action of sulfate, which may be generated from pyrite or solfataric action, on aluminous rocks, commonly accompanied by kaolinitization and silicification.^[95][96]

Association: Kaolinite, halloysite, diaspore, pyrite, gypsum, quartz.^[95]

Alunite has been used for dating (K-Ar method) of weathering processes in ore deposits or of the deposition of alunite in caves.^[96]

Common Impurities: Na,Fe.^[96]

Members of the Alunite Supergroup apparently do not contain Mg or Ni.^[96]

Common associates: Diaspore, Gypsum, Halloysite, Kaolinite, Pyrite, and Quartz.^[96]

Photograph associated minerals: Rodalquilarite, Pyrite, Quartz, Jarosite, Copper, Walfordite, Pyracmonite, Baryte, Enargite, Blatonite.^[96]

File:Ashoverite Milltown Quarry.jpg

Ashoverite is one of three polymorphs of zinc hydroxide, Zn(OH)
₂, a rare mineral first found in a limestone quarry near Ashover, Derbyshire, England, in 1988.^[97]

Ashoverite is trimorphous with sweetite and wülfingite.^[98]

Ashoverite occurs in "a vein in a limestone quarry, on fluorite associated with the polymorphs, sweetite and wulfingite."^[99]

Ashoverite colourless-white tabular crystals are shown in a iron-stained fluorite cavity in the image on the right.

Axinite-(Mg) or magnesioaxinite, Ca₂MgAl₂BOSi₄O₁₅(OH) magnesium rich, can be pale blue to pale violet^[100]

Azurite is a soft, deep-blue copper mineral produced by weathering of copper ore deposits.

During the early 19th century, it was also known as chessylite, after the type locality at Chessy-les-Mines near Lyon, France.^[101] The mineral, a basic carbonate with the chemical formula Cu
₃(CO
₃)
₂(OH)
₂, has been known since ancient times, and was mentioned in Pliny the Elder's Natural History under the Greek name kuanos (κυανός: "deep blue," root of English cyan) and the Latin name caeruleum.^[102] Since antiquity, azurite's exceptionally deep and clear blue has been associated with low-humidity desert and winter skies. The modern English name of the mineral reflects this association, since both azurite and azure are derived via Arabic from the Persian lazhward (لاژورد), an area known for its deposits of another deep-blue stone, lapis lazuli ("stone of azure").

File:Gibbsite polymorphs.png

Bayerite is a polymorph of gibbsite and has the same chemical formula. Part of the challenge of determining the unique structure of bayerite versus gibbsite is that bayerite appears to transform to gibbsite under certain circumstances. The structures may also interleave. The other two polymorphs: nordstrandite and doyleite, are also variations with possible interleaving.

Early structural determinations using powder diffraction studies appeared contradicting.

The first structural study (1942) found bayerite to be hexagonal with two formula units (Z) per unit cell.^[103] The lattice parameters were a=5.01 Å and c=4.76 Å.^[103]

A second study (1951) found bayerite to be monoclinic.^[104]

A third study (1958) found bayerite to be hexagonal with a=5.047 Å and c=4.730 Å with Z=2.^[105]

Doyleite "the mineral from Mont St. Hilaire [is] triclinic, space group P1̅ from morphology, a 5.002(1), b 5.175(1), c 4.980(2) , α 97.50(1), β 118.60(1), γ 104.74(1)°, Z = 2."^[106]

Bayerite has a monoclinic structure and lattice parameters of a=5.062(1) Å, b=8.671(2) Å, c=4.713(1) Å, β =90.27(3)° with space group P2₁/a.^[106]

"The primitive P1̅ unit cell of nordstrandite was confirmed to contain four formula units, unlike doyleite (Z = 2). The layered structures of nordstrandite and doyleite were shown to be closely related to that of bayerite, differing from one another by the interlayer shift vectors only."^[107]

As of 2014, bayerite has the monoclinic (P2₁/m) (or brucite) structure.^[108]

In the diagram on the right, an idealized "structure of gibbsite is projected on (001), showing geometric relations of the cells of gibbsite (solid lines), bayerite (dashed lines), doyleite (dotted lines) and nordstrandite. [Subscripts are] g for gibbsite, d for doyleite and n for nordstrandite. The oxygen atoms are at heights of 0.11 (shaded large circles) and -0.11 (unshaded)."^[106]

Boehmite or böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore bauxite. It is dimorphous with diaspore.

Boehmite occurs in tropical laterites and bauxites developed on alumino-silicate bedrock, occurs as a hydrothermal alteration product of corundum and nepheline, with kaolinite, gibbsite and diaspore in bauxite deposits; and with nepheline, gibbsite, diaspore, natrolite and analcime in nepheline pegmatites.^[109]

Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)
₂. It is a common alteration product of periclase in marble; a low-temperature hydrothermal vein mineral in metamorphosed limestones and chlorite schists; and formed during serpentinization of dunites. Brucite is often found in association with serpentine], calcite, aragonite, dolomite, magnesite, hydromagnesite, artinite, talc and chrysotile.

It adopts a layered CdI₂-like structure with hydrogen-bonds between the layers.^[110]

Calumetite has the chemical formula Cu(OH,Cl)₂·2H₂O.^[15]

Calumetite has been found in association with tremolite, quartz, epidote, monazite, copper, cuprite, atacamite, buttgenbachite, malachite, paratacamite, and anthonyite.^[111]

The specific gravity of calumetite could not be measured because of the difficulty in separating the quartz and epidote from the calumetite mineral coating them.^[112]

Other copper minerals have been linked to calumetite which include copper, cuprite, malachite, atacamite, paratacamite, buttgenbachite.^[112]

Calumetite has been stated to be a naturally occurring mineral.^[113]

Calumetite is insoluble in ammonia and water, and soluble in cold dilute acids.^[112]

Calumetite has been noted to be useful in paintings on canvas and fresco.^[114]

Carrboydite has the formula: (Ni
_(1-x)Al
_x)(SO
₄)
_(x/2)(OH)
₂·nH
₂O, where (x < 0.5, n > 3x/2), is a member of the Glaucocerinite Group > Hydrotalcite Supergroup, in the Hexagonal Crystal System, named for the Carr Boyd nickel mine, Australia, the type locality.^[115]

Carrboydite has the Chemical Formula: (Ni,Cu)
₁₄Al
₉(SO
₄,CO
₃)(OH)
₄₃•7(H
₂O).^[116] The Empirical Formula is Ni
₁₀Cu
₄Al
₉(SO
₄)
₄(CO
₃)
₂(OH)
₄₃•7(H
₂O).^[116]

"As part of the recent re-evaluation of the nomenclature of the hydrotalcite supergroup (Mills et al., 2012), carrboydite was identified as a questionable species which needs further investigation."^[115]

Environment: "Surface material at a nickel mine."^[115]

Doyleite "the mineral from Mont St. Hilaire [is] triclinic, space group P1̅ from morphology, a 5.002(1), b 5.175(1), c 4.980(2) , α 97.50(1), β 118.60(1), γ 104.74(1)°, Z = 2."^[106]

Doyleite grows in small square tabular crystals, which form rosettes. Individual crystals can grow up to 8 mm. The mineral has a layered micaceous structure.^[117]

Some specimens are coated with a thin film of dark brown amorphous material, thought to be iron oxide.^[118]

The hydroxyl group's intra-layer interactions show no Raman scattering in contrast to its polymorphs.^[119]

Doyleite is the least stable of the polymorphs.^[120]

Doyleite is associated with fluorite, zircon, pyrite, albite, siderite and molybdenite.^[117]

Doyleite also occurs with calcite and pyrite in albitite veins.^[106]

Gibbsite, Al(OH)
₃, is one of the mineral forms of aluminium hydroxide, often designated as γ-Al(OH)
₃^[121] (but sometimes as α-Al(OH)₃.^[122]). It is also sometimes called hydrargillite (or hydrargyllite). Doyleite and nordstrandite are triclinic forms.^[121]

The structure of gibbsite is analogous to the basic structure of the micas. The basic structure forms stacked sheets of linked octahedra. Each octahedron is composed of an aluminium ion bonded to six hydroxide groups, and each hydroxide group is shared by two aluminium octahedra.^[123]

Gibbsite is often found as a part of the structure of other minerals. The neutral aluminium hydroxide sheets are found sandwiched between silicate sheets in important clay groups: the illite, kaolinite, and montmorillonite/smectite groups. The individual aluminium hydroxide layers are identical to the individual layers of gibbsite and are referred to as the gibbsite layers.^[124]

Gillardite from 132 North Ni Mine, Widgiemooltha, Coolgardie Shire, Western Australia, Australia has the chemical formula Cu
₃Ni(OH)
₆Cl
₂^[125]

This is a very rare attractive specimen on the right that is just loaded with crystalline gillardite, perched on lighter-green gaspeite. This mineral seldom crystallizes and although small, these crystals are discrete and eye-visible.

Often a mineral appears blue due to the presence of copper or sulfur. Glaucophane is a blue silicate that owes its color to its characteristic formation.

Glaucophane is a mineral belonging to the amphibole group, chemical formula Na
₂Mg
₃Al
₂Si
₈O
₂₂(OH)
₂. The blue color is very diagnostic for this species. It, along with the closely related mineral riebeckite are the only common amphibole minerals that are typically blue. Glaucophane forms in metamorphic rocks that are either particularly rich in sodium or that have experienced low temperature-high pressure metamorphism such as would occur along a subduction zone. This material has undergone intense pressure and moderate heat as it was subducted downward toward the mantle. It is glaucophane's color that gives the blueschist facies its name. Glaucophane is also found in eclogites that have undergone retrograde metamorphism.^[126]

Glaukosphaerites have the CNMMN/CNMNC approved formula: CuNi(CO
₃)(OH)
₂^[127] and the Strunz formula: (Cu,Ni)₂[(OH)₂|CO₃],^[128] or (Cu,Ni)
₂(CO
₃)(OH)
₂.^[129]

It is a member of the Rosasite Group.^[129]

Associated Minerals at Type Locality: Goethite, Quartz, Paratacamite, Gypsum, Magnesite, Malachite, and Clay.^[129]

In the image on the right, hydrohonessite was riginally described as jamborite, now most green coatings on millerite like this have been shown to be hydrohonessite per David Hospital.

Hydrohonessite has the formula: (Ni
_1-xFe³⁺
_x)(OH)
₂(SO
₄)
_x/2 · nH
₂O (x > 0.5, n > ​^3x⁄₂.^[130]

"May convert readily into honessite, depending on humidity and temperature. Appears to be stable between pH 6 and 7."^[130]

General Appearance of Type Material: Thin surface encrustation of tiny hexagonal crystals on botryoidal quartz and magnesite in a fracture in supergene Ni-Fe sulphides.^[130]

Associated Minerals at Type Locality: Quartz, Magnesite, Violarite, Pyrite, Gaspéite, Goethite, Pecoraite and Gypsum.^[130]

"A precipitate corresponding to hydrohonessite was obtained by slowly adding an aqueous 0.1 M ferrous sulphate solution to a 0.1 M nickel sulphate solution. The pH of the solution was maintained between 6.0 and 6.5 by the addition of 0.01 M sodium carbonate. Above pH 7.5, Ni(OH)
₂ is precipitated, and below pH 6, FeOOH. The oxidation of the iron and precipitation of the hydrohonessite is slow, so care must be taken that the pH does not drop too low during the approximately 24 hours that the precipitation requires. After drying at 25°C, the precipitate gives a diffuse X-ray powder pattern similar to that of hydrohonessite. Chemical analysis of the precipitate confirmed that the composition is close to that of hydrohonessite. The infra-red spectrum of the synthetic hydrohonessite [...] is similar to that of honessite (Bish and Livingstone, 1981), and is characterized by strong absorptions due to H
₂O and SO
₄. The synthetic hydrohonessite dehydrates slowly at 25°C, and after ten days it gives a diffuse X-ray diffraction pattern of four lines which correspond to the strongest lines of the honessite diffraction pattern (Bish and Livingstone, 1981), i.e. with a basal spacing in the neighbourhood of 9 Å; the conversion can also be achieved more rapidly by heating the synthetic hydrohonessite at 110°C. The natural hydrohonessite is more stable than its synthetic equivalent, since it retains its integrity at 110°C, and dehydration requires a temperature between 150 and 170°C. The dehydration experiments indicate that hydrohonessite is the hydrated equivalent of honessite."^[131]

Kaolinite has the chemical formula Al
₂Si
₂O
₅(OH)
₄.

Kaolinite is a clay mineral, a layered silicate mineral, with one tetrahedral sheet of silica (SiO
₄) linked through oxygen atoms to one octahedral sheet of alumina (AlO
₆) octahedra.^[132] Rocks that are rich in kaolinite are known as kaolin or porcelain (china) clay.^[133]

The chemical formula for kaolinite as used in mineralogy is Al
₂Si
₂O
₅(OH)
₄,^[134] however, in ceramics applications the formula is typically written in terms of oxides, thus the formula for kaolinite is Al
₂O
₃*2SiO
₂*2H
₂O.^[135]

As the most numerous element is oxygen at 9 for 52.9 at %, kaolin is an oxide.

Kambaldaites have the formula: NaNi
₄(CO
₃)
₃(OH)
₃ · 3H
₂O.^[136]

General Appearance of Type Material: Cryptocrystalline veins, layers and concretionary growths up to about 2 mm thick, commonly intergrown with gaspeite, also as encrustations of tiny hexagonal prisms.^[136]

Geological Setting of Type Material: Nickel sulfide deposit, as a secondary mineral that has been precipitated on fracture surfaces in oxidizing Ni-Fe sulfide ore.^[136]

"The primary sulfides, which occur as assemblages of pentlandite-pyrrhotite-pyrite and pentlandite-millerite-pyrite, have been altered to supergene assemblages consisting largely of violarite and pyrite, which have decomposed on further oxidation to a goethitic residue in which the secondary nickel minerals have been deposited."^[137]

"The samples in which the kambaldaite was found are from a depth of about 20 meters, and consist largely of goethite with some reevesite and residual pyrite. The kambaldaite, together with gaspeite and some aragonite, occurs on fracture surfaces in the goethite. The kambaldaite occurs in a variety of types: massive, crystalline, nodular and chalky."^[137]

Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula: (Na,Ca)
₈[(S,Cl,SO
₄,OH)
₂(Al
₆Si
₆O
₂₄)]. It is a feldspathoid and a member of the sodalite group. The colour is due to the presence of S^3- anions. Lazurite is a product of contact metamorphism of limestone.

Lepidolite (KLi
₂Al(Al,Si)
₃O
₁₀(F,OH)
₂ is a lilac-gray or rose-colored member of the mica group that is a secondary source of lithium, a phyllosilicate mineral^[138] and a member of the polylithionite-trilithionite series.^[139]

It is associated with other lithium-bearing minerals like spodumene in pegmatite bodies. It is one of the major sources of the rare alkali metals rubidium and caesium.^[140]

It occurs in granite pegmatites, in some high-temperature quartz veins, greisens and granites. Associated minerals include quartz, feldspar, spodumene, amblygonite, tourmaline, columbite, cassiterite, topaz and beryl.

Libethenite has the chemical formula Cu
₂PO
₄OH, is a rare copper phosphate hydroxide mineral, that forms striking, dark green orthorhombic crystals, discovered in 1823 in Ľubietová, Slovakia, is named after the German name of that locality (Libethen).^[141][142] Libethenite has also been found in the Miguel Vacas Mine, Conceição, Vila Viçosa, Évora District, Portugal, and in Tier des Carrières, Cahai, Vielsaim, Stavelot Massif, Luxembourg Province, Belgium.^[142]

Libethenite almost always takes the form of dark-green orthorhombic crystals,^[141][142] often found in clusters with other libethenite crystals.

Libethenite is found in the oxidized zone of copper ore deposits,^[142] is most often formed from the weathering of phosphate rocks such as apatite, monazite, and xenotime.^[142] There have been no confirmed findings of primary libethenite, although a probable case has been reported.^[142]

File:Linarite-130513.jpg

Linarite is an monoclinic azure blue mineral with the chemical formula of PbCuSO₄(OH)₂.^[15]

Malachite is a mineral that occurs in rocks at or near the interface between Earth's atmosphere and crust.

Malachite is a copper carbonate hydroxide mineral, with the chemical formula Cu
₂CO
₃(OH)
₂, which is 20 at % copper, 10 at % carbon, 20 at % hydrogen, 50 at % oxygen, 20 molecular % carbonate and 40 molecular % hydroxide.

This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fractures and deep, underground spaces, where the water table and hydrothermal fluids provide the means for chemical precipitation. Individual crystals are rare, but occur as slender to acicular prisms. Pseudomorphs after more tabular or blocky azurite crystals also occur.^[144]

"More like akrochordite is metavauxite (R = 0.097), which is [Fe(H
₂O)²⁺
_6][Al
₂(OH)
₂(H
₂O)
₂(PO
₄)
₂]²⁻
(Baur and Rama Rao, 1967), in that it has insular octahedra alternating with octahedral-tetrahedral sheets separated by the {100} plane. The plane is penetrated by three different hydrogen bonds that are accepted by O(4) of the terminal[PO
₄] tetrahedron of the sheets: OW(7)...O(4) 2.58,OW(7')...O(4) 2.64,and OW(8)...O(4) 2.67 Å. The remaining P-O(4) distance is about the same as the polyhedral average."^[69]

Metavauxite in the image on the right is from Siglo Veinte Mine (Siglo XX Mine; Llallagua Mine; Catavi), Llallagua, Rafael Bustillo Province, Potosí Department, Bolivia.

Microlite is composed of sodium calcium tantalum oxide with a small amount of fluorine (Na,Ca)
₂Ta
₂O
₆(O,OH,F). Microlite is a mineral in the pyrochlore group that occurs in pegmatites and constitutes an ore of tantalum. It has a Mohs hardness of 5.5 and a variable specific gravity of 4.2 to 6.4. It occurs as disseminated microscopic subtranslucent to opaque octahedral crystals with a refractive index of 2.0 to 2.2. Microlite is also called djalmaite. Microlite occurs as a primary mineral in lithium-bearing granite pegmatites, and in miarolitic cavities in granites.

Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. The ideal formula is Ni₃(Si₂O₅)(OH)₄, but most specimens contain some magnesium, and (Ni,Mg)₃(Si₂O₅)(OH)₄ is more realistic. There is a similar mineral called lizardite (named after the Lizard Complex in Cornwall, England) in which all of the nickel is replaced by magnesium, formula Mg₃(Si₂O₅)(OH)₄.^[145] These two minerals form a series; intermediate compositions are possible, with varying proportions of nickel to magnesium.^[146]

"The primitive P1̅ unit cell of nordstrandite [Al(OH)
₃] was confirmed to contain four formula units, unlike doyleite (Z = 2). The layered structures of nordstrandite and doyleite were shown to be closely related to that of bayerite, differing from one another by the interlayer shift vectors only."^[107]

"In nature there exists [the] hydroxy nickel carbonate [mineral] nullaginite Ni
₂(CO
₃)(OH)
₂^1-3 [...] Nullaginite is monoclinic with point group 2/m and is a member of the rosasite mineral group. Nullaginite is formed in the oxidised zone of nickel rich hydrothermal ore deposits."^[147]

Olivenite is a copper arsenate mineral has the chemical formula Cu
₂AsO
₄OH crystallizes in the monoclinic system (pseudo-orthorhombic),^[148] is a mineral of secondary origin, a result of the oxidation of copper ores and arsenopyrite.

The mineral was formerly found in some abundance, associated with limonite and quartz, in the upper workings in the copper mines of the St Day district in Cornwall; also near Redruth, and in the Tintic Mining District in Utah.

The arsenic of olivenite is sometimes partly replaced by a small amount of phosphorus, and in the species libethenite we have the corresponding copper phosphate Cu
₂PO
₄OH, found as small dark green crystals resembling olivenite at Ľubietová in the Slovak Republic, and in small amount also in Cornwall. Other members of this isomorphous group of minerals are adamite, Zn
₂AsO
₄OH, and eveite, Mn
₂AsO
₄OH.

Otwayite has the chemical formula Ni
₂CO
₃(OH)
₂.^[147]

Otwayite has the formula: Ni
₂CO
₃(OH)
₂ · H
₂O.^[149]

Geological Setting of Type Material: Narrow veinlets to 1 mm in width, probably late-stage fracture filling, transecting nickeloan serpentine, millerite, polydymite, and apatite.^[149]

Otwayite is associated with Widgiemoolthalite.^[149]

Occurrence: Otwayite is found in association with nullaginite and hellyerite in the Otway nickel deposit, is found in association with theoprastite, hellyerite, gaspeite and a suite of other nickel carbonate minerals in the Lord Brassey Mine, Tasmania, in association with gaspeite, hellyerite and kambaldaite in the Widgie Townsite nickel gossan, Widgiemooltha, Western Australia, and reported from the Pafuri nickel deposit, South Africa.^[150]

It was first described in 1977 from the Otway Nickel Deposit, Nullagine, Pilbara Craton, Western Australia and named for Australian prospector Charles Albert Otway (born 1922).^[151]

Paratacamite has the chemical formula Cu
₃(Cu,Zn)(OH)
₆Cl
₂.^[152]

A very rich specimen of microcrystalline, brilliant green paratacamite crystals - exceedingly rich from the locality. Ex. Richard Barstow Collection.

Paravauxites have the formula Fe²⁺
Al
₂(PO
₄)
₂(OH)
₂ · 8H
₂O.^[153]

Paravauxite is a rare mineral that was named in 1922, a portmanteau word made by blending the Greek word for near (παρα, meaning para) and vauxite due to the chemical relationship to vauxite, approved by the International Mineralogical Association (IMA), and was first described in 1959, grandfathered, meaning it is probably to remain a species.^[153]

It is a member of the laueite supergroup, and the laueite group within said supergroup, a metavauxite triclinic dimorph that can form in complex granitic pegmatites, and in hydrothermal tin veins. It forms thick tabular crystals on {010}, and short prismatic ones on [001], but numerous forms might be exhibited. Forms aggregates that are subparallel to radial. The mineral is colorless in transmitted light.^[153] It mainly consists of oxygen (60.26%), but contains phosphorus (12.96%), iron (11.69%), aluminum (11.29%) and hydrogen (3.80%) as well. It doesn't show any radioactive properties whatsoever.^[154] It occurs in tin mines. Paravauxite has a vitreous luster, with one exception on b(100), where it is pearly. It grows in small crystals, which's size can reach up to 5×2×1.5 mm. Crystals are somewhat flattened parallel to b(100). Even with atmospheric humidity, paravauxite's hydrogen dioxide content varies considerably. The mineral's formula is complex, that's why it's really unlikely that it gets simplified by further analyses. There's only one occurrence where vauxite and paravauxite are seen together in one specimen. It's a small, cavernous, mass of druzy-green wavellite. It has blue vauxite in small radial aggregates, and a singular colorless paravauxite. One of blue vauxite's radial aggregates has this crystal implanted on top.^[155]

Other than vauxite and metavauxite, it is also associated with wavellite, but rarely occurs on the latter, the type locality of Llallagua, Bolivia.^[154] It can also be found in Germany, Mexico, the United States, Portugal, Sweden, with a couple of other countries.^[156]

"Paravauxite can be found in association with vauxite, metavauxite, wavellite, sigloite, crandallite, childrenite, and quartz."^[157]

Pecoraite is a nickel phyllosilicate^[158] mineral and a member of the Serpentine Subgroup > Kaolinite-Serpentine Group, named after geologist William Thomas Pecora, is monoclinic and has a chemical composition of Ni
₃(Si
₂O
₅)(OH)
₄.^[159]

Common Impurities: Al, Fe, Mg, Ca, H
₂O.^[159]

Geological Setting of Type Material: Weathered meteorite.^[159]

Geological setting: Shears in ultramafic rocks, weathering product of millerite in geodes.^[159]

Pecoriate is typically a green, lime green, or bluegreen mineral with a waxy, or earthy luster and a mohs hardness of 2.5.^[158]

Morphology: curved plates, spirals and tubes, granular and massive.^[159]

Pectolite is a white to gray mineral, NaCa
₂Si
₃O
₈(OH), sodium calcium hydroxide inosilicate that crystallizes in the triclinic system typically occurring in radiated or fibrous crystalline masses, has a Mohs hardness of 4.5 to 5 and a specific gravity of 2.7 to 2.9. The gemstone variety, larimar, is a pale to sky blue.

Occurrence: It was first described in 1828 at Mt. Baldo, Trento Province, Italy, and named from the Greek pektos – "compacted" and lithos – "stone".^[160][161]

Occurrence: as a primary mineral in nepheline syenites, within hydrothermal cavities in basalts and diabase and in serpentinites in association with zeolites, datolite, prehnite, calcite and serpentine. It is found in a wide variety of worldwide locations.

Pectolite is found in many locations, but larimar has a unique volcanic blue coloration, which is the result of copper substitution for calcium.^[162]

Miocene volcanic rocks, andesites and basalts, erupted within the limestones of the south coast of the island, contained cavities or vugs which were later filled with a variety of minerals, including the blue pectolite, which are a secondary occurrence within the volcanic flows, dikes, and plugs, which erode, the pectolite fillings are carried down the slope to end up in the alluvium and the beach gravels, and the Bahoruco River carried the pectolite-bearing sediments to the sea.^[163]

Larimar is a copper substituted for calcium NaCu
₂Si
₃O
₈(OH) pectolite, a rare blue variety of the silicate mineral pectolite found only in the Dominican Republic, in the Caribbean]]. Its coloration varies from white, light-blue, green-blue to deep blue.^[163]

Portlandite is a hydroxide-bearing mineral typically included in the oxide mineral class, the naturally occurring form of calcium hydroxide Ca(OH)
₂ and the calcium analogue of brucite Mg(OH)
₂.

Portlandite occurs in a variety of environments. At the type location in Northern Ireland it occurs as an alteration of calc–silicate rocks by contact metamorphism of larnite–spurrite. as fumarole deposits in the Vesuvius area, in Jebel Awq, Oman, it occurs as precipitates from an alkaline spring emanating from ultramafic bedrock, in the Chelyabinsk coal basin of Russia it is produced by combustion of coal seams and similarly by spontaneous combustion of bitumen in the Hatrurim Formation of the Negev desert in Israel and the Maqarin area, Jordan.^[164] It also occurs in the manganese mining area of Kuruman, Cape Province, South Africa in the Kalahari Desert where it occurs as large crystals and masses.^[165][164]

It occurs in association with afwillite, calcite, larnite, spurrite, halite, brownmillerite, hydrocalumite, mayenite and ettringite.^[164]

It was first described in 1933 for an occurrence at Scawt Hill, Larne, County Antrim, Northern Ireland. It was named portlandite because the chemical calcium hydroxide is a common hydrolysis product of Portland cement.^[165][164]

Chemical Formula: Ni
₆Fe³⁺
₂(CO
₃)(OH)
₁₆•4(H
₂O).^[166]

Environment: Alteration product of a highly weathered iron-nickel meteorite.^[166]

Type Locality: Wolf Creek meteorite, found three km west of the Scotia talc mine, Bon Accord area, Barberton, Transvaal, South Africa.^[166]

Crystal System: Trigonal.^[167]

Member of the Hydrotalcite Group > Hydrotalcite Supergroup.^[167]

Geological Setting: Nickel rich ore deposits.^[167]

Geological Setting of Type Material: alteration product of a highly weathered iron-nickel meteorite.^[167]

Associated Minerals at Type Locality: Goethite, Jarosite, Serpentine Subgroup, Apatite, Lipscombite.^[167]

1. Formula: (Ba,H
   ₂O)
   ₂(Mn⁴⁺
   ,Mn³⁺
   )
   ₅O
   ₁₀.^[168]
2. Crystal system: monoclinic.^[168]
3. Colour: Greyish black, black.^[168]
4. Lustre: Sub-Metallic, Dull.^[168]
5. Hardness: 5 - 6.^[168]

Romanèchite is the primary constituent of psilomelane, which is a mixture of minerals.

Satterlyite is a hydroxyl bearing iron phosphate mineral. The mineral can be found in phosphatic shales. Satterlyite is part of the phosphate mineral group. Satterlyite is a transparent, light brown to light yellow mineral. Satterlyite has a formula of (Fe²⁺,Mg,Fe³⁺)₂(PO₄)(OH). Satterlyite occurs in nodules in shale in the Big Fish River (Mandarino, 1978). These nodules were about 10 cm in diameter, some would consist of satterlyite only and others would show satterlyite with quartz, pyrite, wolfeite or maricite.

Holtedahlite, a mineral that was found in Tingelstadtjern quarry in Norway, with the formula (Mg₁₂PO₄)₅(PO₃OH,CO₃)(OH,O)₆ is isostructural with satterlyite (Raade, 1979). Infrared absorption powder spectra show that satterlyite is different than natural haltedahlite in that there is no carbonate for phosphate substitution (Kolitsch, 2002). Satterlyite is also structurally related to phosphoellenbergerite, a mineral that was discovered in Modum, Norway; near San Giocomo Vallone Di Gilba, in Western Alps of Italy (Palache, 1951); the minerals formula is Mg₁₄(PO₄)₅(PO₃OH)₂(OH)₆ (Kolitsch, 2002).

The mineral of the formula Cu(OH)
₂ is called spertiniite.

Copper(II) hydroxide is rarely found as an uncombined mineral because it slowly reacts with carbon dioxide from the atmosphere to form a basic copper(II) carbonate. Thus copper slowly acquires a dull green coating in moist air by the reaction:

2Cu(OH)
₂ + CO
₂ → Cu
₂CO
₃(OH)
₂ + H
₂O

The green material is in principle a 1:1 mole mixture of Cu(OH)
₂ and CuCO
₃.^[169]

Stevensite has the chemical formula (Ca,Na)
_xMg
_3-xSi
₄O
₁₀(OH)
₂ and crystallizes in the Monoclinic system.

File:Sweetite Milltown Quarry.jpg

Sweetite has a general formula of Zn(OH)
₂.^[170] The name is given after a curator of mineral department of The British Museum, Jessie May Sweet (1901–1979).^[171] It occurs in an oxidized vein in limestone bedrock with galena, ashoverite, wülfingite, anglesite, cerussite, hydrocerussite, litharge, fluorite, palygorskite and calcite.^[172]

Sweetite is tetragonal, which means crystallographically it contains one axis of unequal length and two axes of equal length. The angles between three of the axes are all 90°. It belongs to the space group 4/m. Some crystals show evidence of a basal plane and a few are tabular.^[173] In terms of its optical properties, sweetite has two indices of refraction, 1.635 along the ordinary ray and 1.628 along the extraordinary ray.^[171] The index of refraction is the velocity of light in a vacuum divided by the velocity of light in medium. It also has the birefringence of 0.007.^[174] The birefringence means the decomposition of light into two rays when passing through a mineral. Sweetite is 1.64 - 1.65 in relief, which is medium to high in intensity and means a measure of the relative difference between the index of refraction of a mineral and its surrounding medium.^[170]

Sweetite is mostly found from a limestone quarry 200–300 m northwest of Milltown, near Ashover, Derbyshire, England.^[172]

Takovites have the formula: Ni
₆Al
₂(OH)
₁₆(CO
₃) · 4H
₂O.^[175]

Member of the Hydrotalcite Group > Hydrotalcite Supergroup.^[175]

Morphology: Microcrystalline, platy, to 1 µm; commonly in veinlets and massive.^[175]

Turquoise at right is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminium, with the chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O.

The IMA-CNMNC approved mineral symbol is Ubz.^[6]

Umbozerites have the chemical formula Na
₃Sr
₄Th[Si(O,OH
_(3-4)]
₈, IMA formula Na
₃Sr
₄ThSi
₈(O,OH)
₂₄, common impurities: Ti,Ce,Fe,U,Mn,Ca,Ba,K, and Crystal System: Amorphous.^[176]

Environment: In ussingite veinlets cutting alkalic rocks, type locality: Umbozero (Lake Umba), Kola Peninsula, Russia, dark brown prismatic umbozerite masses in pegmatite rock, Metamict - Mineral originally crystalline, now amorphous due to radiation damage, Pseudo Tetragonal - Crystals show a tetragonal shape, Umbozerite is Radioactive as defined in 49 CFR 173.403, greater than 70 Bq / gram.^[177]

Occurrence: In pneumatolytic-hydrothermal veins cutting alkalic rocks in the upper part of a differentiated alkalic massif, Crystal Data: Metamict; tetragonal after recrystallization^[178]

Association: Ussingite, sphalerite, belovite, manganoan pectolite, lorenzenite, niobium-bearing minerals of the lomonosovite group.^[178]

Distribution: Found on Mts. Karnasurt and Punkaruaiv, near Lake Umba, Lovozero massif, Kola Peninsula, Russia.^[178]

Uranophane Ca(UO
₂)
₂(SiO
₃OH)
₂·5H
₂O is a rare calcium uranium [nesosilicate] hydrate mineral that forms from the oxidation of uranium bearing minerals. Uranophane is also known as uranotile. It has a yellow color and is radioactive.

"Widgiemoolthalite is a rare hydrated nickel(II) carbonate mineral with the chemical formula (Ni,Mg)₅(CO₃)₄(OH)₂·5H₂O. Usually bluish-green in color, it is a brittle mineral formed during the weathering of nickel sulfide. Present on gaspéite surfaces".^[179]

Falcondoite and willemseite in the image on the right are rare nickel, magnesium silicates found in a serpentinized harzbergite massif or an obducted ophiolite at a plate collision of oceanic crust with continental crust. The locality is in the Dominican Republic, which is the Type Locality for falcondoite. This very showy, bright green thin crust is mostly green falcondoite, with just a bit of lighter, olive willemseite.

Wllemseite has the chemical formula Ni
₃Si
₄O
₁₀(OH)
₂.

File:Zoisite-variety-tanzanite-05.jpg

Tanzanite, a variety of zoisite that is purple-blue member of the epidote group.^[15]

On the right is both a rough stone and a cut stone of tanzanite. Tanzanite is the blue/purple variety of the mineral zoisite (a calcium aluminium hydroxy silicate) with the formula (Ca₂Al₃(SiO₄)(Si₂O₇)O(OH))]. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet and burgundy depending on crystal orientation.^[180] Tanzanite can also appear differently when viewed under alternate lighting conditions. The blues appear more evident when subjected to fluorescent light and the violet hues can be seen readily when viewed under incandescent illumination. A rough violet sample of tanzanite is third down at left.

Tanzanite in its rough state is usually a reddish brown color. It requires artificial heat treatment to 600 °C in a gemological oven to bring out the blue violet of the stone.^[181]

Tanzanite is found only in the foothills of Mount Kilimanjaro.

Tanzanite is universally heat treated in a furnace, with a temperature between 550 and 700 degrees Celsius, to produce a range of hues between bluish-violet to violetish-blue. Some stones found close to the surface in the early days of the discovery were gem-quality blue without the need for heat treatment.

Zoisite has the chemical formula Ca₂Al₃Si₃O₁₂OH.^[15]

1. Variations in rocks from one mineral composition into another can occur with each rock type.
2. Oxidanes that are various ices may be produced by orbital cycling.

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