# Geominerals/Sulfates

The sulfide ion, S$^{2−}$ , does not exist in aqueous alkaline solutions of Na $_2$S. Instead sulfide converts to hydrosulfide:
    S$^{2−}$ + H $_2$O → SH$^−$ + OH$^−$
Upon treatment with an acid, sulfide salts convert to hydrogen sulfide:
    S$^{2−}$ + H$^+$ → SH$^−$
    SH$^−$ + H$^+$ → H $_2$S
* Combustion: 2H $_2$S + 3O $_2$ ⇌ 2H $_2$O + 2SO $_2$ (-1036 kJ/mol)
* Oxidation: 2SO $_2$ + O $_2$ ⇌ 2SO $_3$ (-198 kJ/mol) [in the presence of a vanadium (V) oxide catalyst, e.g., vanadium pentoxide V $_2$O $_5$]
* Hydration: SO $_3$ + H $_2$O ⇌ H $_2$SO $_4$ (g) (-101 kJ/mol)
* Condensation: H $_2$SO $_4$ (g) ⇌ H $_2$SO $_4$ (l) (-90 kJ/mol)
Oxidation of sulfide depends on the conditions, the oxidation can produce elemental sulfur, polysulfides, polythionates, sulfite, or sulfate.
Methods of preparing metal sulfates include:
    Zn + H $_2$SO $_4$ → ZnSO $_4$ + H $_2$
    Cu(OH) $_2$ + H $_2$SO $_4$ → CuSO $_4$ + 2H $_2$O
    CdCO $_3$ + H $_2$SO $_4$ → CdSO $_4$ + H $_2$O + CO $_2$

## Afghanites

Afghanite is a Tectosilicate with the chemical formula (Na,K) $_{22}$Ca $_{10}$[Si $_{24}$Al $_{24}$O $_{96}$](SO $_4$) $_6$Cl $_6$, symmetry: P31c is a hydrous sodium, calcium, potassium, sulfate, chloride, carbonate, alumino-silicate mineral, is a feldspathoid of the cancrinite group and typically occurs with sodalite group minerals, has IMA symbol is Afg, forms blue to colorless, typically massive crystals in the trigonal crystal system. The lowering of the symmetry from typical (for cancrinite group) hexagonal one is due to ordering of Si and Al. It has a Mohs hardness of 5.5 to 6 and a specific gravity of 2.55 to 2.65. It has refractive index values of nω=1.523 and nε=1.529. It has one direction of perfect cleavage and exhibits conchoidal fracture. It fluoresces a bright orange.
It was discovered in 1968 in the Lapis-lazuli Mine, Sar-e-Sang, Badakhshan Province, Afghanistan and takes its name from that country. It has also been described from localities in Germany, Italy, the Pamir Mountains of Tajikistan, near Lake Baikal in Siberia, New York and Newfoundland. It occurs as veinlets in lazurite crystals in the Afghan location and in altered limestone xenoliths within pumice in Pitigliano, Tuscany, Italy.

## Alum-(K)s

Alum-(K) is a hydrous potassium aluminium sulfate mineral with formula KAl(SO $_4$) $_2$·12(H $_2$O). It's International Mineralogical Association (IMA) symbol is Aum-K. It is the mineral form of potassium alum and is referred to as potassium alum in older sources. It is a member of the alum group.
It occurs as colorless to white, soft isometric crystals and efflorescence coatings. Rare crystals are octahedral in form if occurring as precipitates from neutral water solution, but cubic in form if the solution is alkaline.
It occurs as a precipitate around volcanic fumaroles and solfataras. It also occurs as an alteration in argillaceous sediments or coal beds which contain oxidizing sulfide minerals (pyrite or marcasite). Occurs associated with alunogen, pickeringite, epsomite, melanterite, gypsum and native sulfur.
Occurrences include Mount Vesuvius, Italy and Alum Cave, Sevier County, Tennessee.

## Aluminites

Chemical formula: Al $_2$(SO $_4$)(OH) $_4$•7H $_2$O.
Crystal system: Monoclinic.
Member of the Aluminite Group.
Other Members of this group: Mangazeite Al $_2$(SO $_4$)(OH) $_4$·3H $_2$O.
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."
"Found as earthy reniform or nodular masses composed of tiny fibrous crystals."
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."
Association: "Basaluminite, gibbsite, epsomite, gypsum, celestine, dolomite, goethite."

## Alunites

Alunite (International Mineralogical Association (IMA) symbol: Alu) is a hydroxylated aluminium potassium sulfate mineral, formula KAl $_3$(SO $_4$) $_2$(OH) $_6$.
Polymorphism & Series: Forms a series with natroalunite.
Mineral Group: Alunite group.
Alunite Group > Alunite Supergroup.
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.
Association: Kaolinite, halloysite, diaspore, pyrite, gypsum, quartz.
Alunite has been used for dating (K-Ar method) of weathering processes in ore deposits or of the deposition of alunite in caves.
Common Impurities: Na,Fe.
Members of the Alunite Supergroup apparently do not contain Mg or Ni.
Common associates: Diaspore, Gypsum, Halloysite, Kaolinite, Pyrite, and Quartz.
Photograph associated minerals: Rodalquilarite, Pyrite, Quartz, Jarosite, Copper, Walfordite, Pyracmonite, Baryte, Enargite, Blatonite.

## Alunogens

Alunogen is a colourless to white (although often coloured by impurities, such as iron substituting for aluminium) fibrous to needle-like aluminium sulfate mineral with the International Mineralogical Association (IMA) symbol of Alg, and the chemical formula Al $_2$(SO $_4$) $_3$·17H $_2$O.
Occurrence: Forms by reaction of sulfates from decomposing sulfides with aluminous minerals in shales and slates; in gossan or altered wall rock of pyritic deposits in arid regions; in coal seams; in relatively low-temperature fumaroles.
Environment: Secondary mineral commonly associated with coals and pyritiferous shales in arid regions.
Alunogen is often found on the walls of mines and quarries as a secondary mineral, in the oxidation zones of some ore deposits as well as on burning coal dumps (i.e., as the product of millosevichite hydration), forms as a low temperature deposit in fumaroles, and occurs associated with pyrite, marcasite, halotrichite, pickeringite, epsomite, potash alum, melanterite and gypsum.
"At high temperates, alunogen may dehydrate to its pentahydrate, Unnamed (Al Sulphate-Hydrate)."
The crystallochemical formula, can be written as: [Al(H $_2$O) $_6$] $_2$(SO $_4$) $_3$.5H $_2$O. The second formula shows that H $_2$O in the alunogen formula occurs both as a ligand (coordinative form) and a loosely bound (crystallization) form.

## Boussingaultites

(NH $_4$) $_2$Mg(SO $_4$) $_2$·6H $_2$O.

## Carrboydites

Carrboydite has the formula: (Ni $_{(1-x)}$Al $_x$)(SO $_4$) $_{(x/2)}$(OH) $_2$·nH $_2$O, 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.
Carrboydite has the Chemical Formula: (Ni,Cu) $_{14}$Al $_9$(SO $_4$,CO $_3$)(OH) $_{43}$•7(H $_2$O). The Empirical Formula is Ni $_{10}$Cu $_4$Al $_9$(SO $_4$) $_4$(CO $_3$) $_2$(OH) $_{43}$•7(H $_2$O).
"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."
Environment: "Surface material at a nickel mine."

## Chalcanthites

CuSO $_4$·5H $_2$O.

## Copiapites

Fe$^{2+}$ Fe$^{3+}$ $_4$(SO $_4$) $_6$(OH} $_2$·20H $_2$O.

## Copper-bearing melanterites

(Fe,Cu)SO $_4$·7H $_2$O.

## Coquimbites

AlFe $_3$(SO $_4$) $_6$(H $_2$O) $_{12}$·6H $_2$O.

## Cyanochroites

K $_2$Cu(SO $_4$) $_2$·6H $_2$O.

## Epsomites

MgSO $_4$·7H $_2$O.

## Gypsums

CaSO $_4$·2H $_2$O.

## Halotrichites

FeAl $_2$(SO $_4$) $_4$·22H $_2$O.

## Hauynes

Hauyne, haüyne or hauynite occurs in Vesuvian lavas in Monte Somma, Italy. It is a tectosilicate mineral with sulfate, with endmember formula Na $_3$Ca(Si $_3$Al $_3$)O $_{12}$(SO $_4$). It is a feldspathoid and a member of the sodalite group. Haüyne occurs in phonolites and related leucite- or nepheline-rich, silica-poor, igneous rocks; less commonly in nepheline-free extrusives and metamorphic rocks (marble).

## Honessites

Honessite has the formula: (Ni $_{1-x}$Fe$^{3+}$ $_x$)(OH) $_2$(SO $_4$) $_{x/2}$ · nH $_2$O (x < 0.5, n > ​$^{3x}$⁄$_2$.

## Hydrohonessites

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 $_{1-x}$Fe$^{3+}$ $_x$)(OH) $_2$(SO $_4$) $_{x/2}$ · nH $_2$O (x > 0.5, n > ​$^{3x}$⁄$_2$.
"May convert readily into honessite, depending on humidity and temperature. Appears to be stable between pH 6 and 7."
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.
Associated Minerals at Type Locality: Quartz, Magnesite, Violarite, Pyrite, Gaspéite, Goethite, Pecoraite and Gypsum.
"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 $_2$O 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."

## Katerinopoulosites

(NH $_4$) $_2$Zn(SO $_4$) $_2$·6H $_2$O.

## Lazurites

Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula: (Na,Ca) $_8$[(S,Cl,SO $_4$,OH) $_2$(Al $_6$Si $_6$O $_{24}$)]. 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.

## Mbobomkulites

(Ni,Cu)Al $_4$((NO $_3$) $_2$,SO $_4$)(OH) $_{12}$·3H $_2$O.

## Melanterites

Fe$^{2+}$ (H $_2$O) $_6$SO $_4$·H $_2$O.

## Meta-alunogens

Al $_2$(SO $_4$) $_3$·12H $_2$O.

## Metavoltines

K $_2$Na $_6$Fe$^{2+}$ Fe$^{3+}$ $_6$O $_2$(SO $_4$) $_{12}$·18H $_2$O.

## Millosevichites

Millosevichite is a rare sulfate mineral with the chemical formula Al $_2$(SO $_4$) $_3$.
The mineral is mainly known from burning coal dumps, acting as one of the main minerals forming sulfate crust, also found in volcanic solfatara environments.
Compare also sulfalumite, the Al analogue of mikasaite and structurally related to koryakite.

## Mohrites

(NH $_4$) $_2$Fe(SO $_4$) $_2$·6H $_2$O.

## Morenosites

The heptahydrate nickel sulfate NiSO $_4$.7H $_2$O, which is relatively unstable in air, occurs as morenosite.
"On standing in the open in dry air, crystals of morenosite generally dehydrate rapidly to the tetragonal hexahydrate, retgersite. This was verified by the writers on several artificial preparations. The product formed, however, varies considerably with circumstances. One artificial preparation, crystallized from a water solution containing a little HCl, proved to be stable under ordinary conditions. Further, the natural morenosite from Minasragra had partially effloresced during the thirty years or so that it had been contained in the collection, but the dehydration product proved to be not the hexahydrate but a mixture of several lower hydrates."
A "complete series extends between the orthorhombic compounds morenosite, NiSO $_4$·7H $_2$O, and epsomite, MgSO $_4$·7H $_2$O, as shown by Dufet (5) and by Hutton (10)."
"Retgersite can be synthesized by crystallization from pure water solution at temperatures between 31.5°, below which orthorhombic NiSO $_4$·7H $_2$O is stable, and 53.3°, above which monoclinic NiSO $_4$·6H $_2$O is stable. A dihydrate forms above about 118°. These transition temperatures are from the data of Steele and Johnson (17); slightly different values have been reported by others (see Seidell (17)), and metastable equilibria commonly occur. Retgersite also can crystallize at temperatures at least as low as 0° from solutions which contain an appropriate excess of free H $_2$SO $_4$, as shown by Rohmer (14) and others. This factor may determine its formation in nature in place of morenosite. Under certain circumstances both retgersite and morenosite have been observed to crystallize simultaneously, one or the other of the two compounds being in metastable equilibrium."

## Nickelalumites

Formula: (Ni,Cu)Al $_4$(SO $_4$,(NO $_3$) $_2$)(OH) $_{12}$·3H $_2$O.
"Originally reported from Mbobo Mkulu Cave, Nelspruit District, Mpumalanga Province, South Africa."
Crystal System: Monoclinic.

## Nickelblödites

Nickelblödite is a rare nickel sulfate mineral with the formula Na $_2$Ni(SO $_4$) $_2$·4H $_2$O. Nickelblödite was discovered in nickel mines in Carr Boyd Rocks and Kambalda, Western Australia. The mineral is a nickel-analogue of blödite, changoite, cobaltoblödite and manganoblödite - other representatives of the blödite group.
Nickelblödite contains small admixtures of magnesium and iron.
Minerals associating with nickelblödite include violarite, morenosite, halite, pyrite, and siderite.

## Nickelboussingaultites

(NH $_4$) $_2$Ni(SO $_4$) $_2$·6H $_2$O.

## Nickelpicromerites

K $_2$Ni(SO $_4$) $_2$·6H $_2$O.

## Pickeringites

MgAl $_2$(SO $_4$) $_4$·22H $_2$O.

## Retgersites

Aqueous solutions of nickel sulfate react with sodium carbonate to precipitate nickel carbonate, a precursor to nickel-based catalysts and pigments. Addition of ammonium sulfate to concentrated aqueous solutions of nickel sulfate precipitates Ni(NH$_4$)$_2$(SO$_4$)$_2$·6H$_2$O, a blue-coloured solid analogous to Mohr's salt, Fe(NH$_4$)$_2$(SO$_4$)$_2$·6H$_2$O.
Nickel sulfate occurs as the rare mineral retgersite, which is a hexahydrate.
"Oxidization zone of nickel-bearing hydrothermal mineral deposits, formed from H $_2$O solution between 31.5 deg C and 53.5 deg C. Dimorphous with nickelhexahydrite."
The second hexahydrate is known as nickel hexahydrite (Ni,Mg,Fe)SO$_4$·6H$_2$O.
"May occur as a dehydration product of morenosite."
"The tetragonal polymorph of NiSO $_4$•6H $_2$O was first identified [...] as poorly formed, bluish green crystals incrusting a black coke-like mass of patronite from Minasragra, Peru."
Natural "occurrences of retgersite [...] comprised a foot-long mass of niccolite-bearing vein material from a mine in Cottonwood Canyon, Churchill County, Nevada [...]. The geology of the deposit has been described by Ferguson (6). The specimen has been thoroughly oxidized and is crusted over and veined by apple-green, granular masses of annabergite and blue-green fibrous aggregates of retgersite. The retgersiteis an original deposit, in part earlier formed than annabergite, and is not a dehydration product of morenosite."
"The Mg and part at least of the Fe$^{2+}$ is present in substitution for Ni."
"Retgersite is isostructural with the tetragonal polymorphs of the hexahydrated selenates of Ni and Zn."
"The monoclinic polymorph of NiSO $_4$•6H $_2$O has been prepared artificially and its crystallographic and optical properties have been described (8,9). This compound, green in color, is formed from pure water solutions at temperatures over 53.3°C. and below this temperature rapidly inverts to the blue tetragonal polymorph. The occurrence of this unstable and relatively soluble (52.5g. NiSO $_4$ in 100g. water at 54.5°) monoclinic phase in nature seems very unlikely. The monoclinic zinc and magnesium analogues are stable under ordinary conditions, however, and occur in nature as the minerals bianchite and hexahydrite."
The heptahydrate, which is relatively unstable in air, occurs as morenosite.
The monohydrate occurs as very rare mineral dwornikite (Ni,Fe)SO$_4$·H$_2$O.

## Römerites

Fe$^{2+}$ Fe$^{3+}$ $_2$(SO $_4$) $_4$·14H $_2$O.

## Schönites

Chemical formula: K $_2$Mg(SO $_4$) $_2$·6H $_2$O.
Picromerite (synonyms: schoenite, schönite) is a mineral from the class of hydrous sulfates lacking additional anions, and containing medium to large cations according to the Nickel–Strunz classification.
Picromerite is found in comparatively few places, currently (2015) only about 40 localities are known. It was first identified in active volcanic fumaroles on Mount Vesuvius by Arcangelo Scacchi in 1855.
"Fresh picromerite is colorless. Specimens may dehydrate in collections within days to years (according to the conditions) to white, opaque leonite."
Geological Setting: In kainite zones of some oceanic salt deposits.
Association: "Halite, anhydrite, kainite, epsomite (oceanic salt deposits); hohmannite, metavoltine, metasideronatrite (Chuquicamata, Chile)."

## Voltaites

K $_2$Fe$^{2+}$ $_5$Fe$^{3+}$ $_3$Al(SO $_4$) $_{12}$·18H $_2$O.

## Hypotheses

* Most minerals on Earth are oxides.