Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk chalk. Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite. The Mohs scale of mineral hardness defines gypsum as hardness value 2 based on scratch hardness comparison.
Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate (BaSO4). Baryte is generally white or colorless, and is the main source of the element barium. The baryte group consists of baryte, celestine (strontium sulfate), anglesite (lead sulfate), and anhydrite (calcium sulfate). Baryte and celestine form a solid solution (Ba,Sr)SO4.
Strontianite (SrCO3) is an important raw material for the extraction of strontium. It is a rare carbonate mineral and one of only a few strontium minerals. It is a member of the aragonite group.
A geode is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter are secluded. The crystals are formed by the filling of vesicles in volcanic and subvolcanic rocks by minerals deposited from hydrothermal fluids; or by the dissolution of syn-genetic concretions and partial filling by the same or other minerals precipitated from water, groundwater, or hydrothermal fluids.
Niter or nitre is the mineral form of potassium nitrate, KNO3. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits.
Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum. It has many uses in industry. All forms are white solids that are poorly soluble in water. Calcium sulfate causes permanent hardness in water.
Anglesite is a lead sulfate mineral with the chemical formula PbSO4. It occurs as an oxidation product of primary lead sulfide ore, galena. Anglesite occurs as prismatic orthorhombic crystals and earthy masses, and is isomorphous with barite and celestine. It contains 74% of lead by mass and therefore has a high specific gravity of 6.3. Anglesite's color is white or gray with pale yellow streaks. It may be dark gray if impure.
Anhydrite, or anhydrous calcium sulfate, is a mineral with the chemical formula CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium (baryte) and strontium (celestine) sulfates, as might be expected from the chemical formulas. Distinctly developed crystals are somewhat rare, the mineral usually presenting the form of cleavage masses. The Mohs hardness is 3.5, and the specific gravity is 2.9. The color is white, sometimes greyish, bluish, or purple. On the best developed of the three cleavages, the lustre is pearly; on other surfaces it is glassy. When exposed to water, anhydrite readily transforms to the more commonly occurring gypsum, (CaSO4·2H2O) by the absorption of water. This transformation is reversible, with gypsum or calcium sulfate hemihydrate forming anhydrite by heating to around 200 °C (400 °F) under normal atmospheric conditions. Anhydrite is commonly associated with calcite, halite, and sulfides such as galena, chalcopyrite, molybdenite, and pyrite in vein deposits.
The mineral marcasite, sometimes called "white iron pyrite", is iron sulfide (FeS2) with orthorhombic crystal structure. It is physically and crystallographically distinct from pyrite, which is iron sulfide with cubic crystal structure. Both structures contain the disulfide S22− ion, having a short bonding distance between the sulfur atoms. The structures differ in how these di-anions are arranged around the Fe2+ cations. Marcasite is lighter and more brittle than pyrite. Specimens of marcasite often crumble and break up due to the unstable crystal structure.
Afghanite, (Na,K)22Ca10[Si24Al24O96](SO4)6Cl6, is a hydrous sodium, calcium, potassium, sulfate, chloride, carbonate alumino-silicate mineral. Afghanite is a feldspathoid of the cancrinite group and typically occurs with sodalite group minerals. It 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.
Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named thomsonite-Ca and thomsonite-Sr. Thomsonite-Ca, by far the more common of the two, is a hydrous sodium, calcium and aluminium silicate, NaCa2Al5Si5O20·6H2O. Strontium can substitute for the calcium and the appropriate species name depends on the dominant element. The species are visually indistinguishable and the series name thomsonite is used whenever testing has not been performed. Globally, thomsonite is one of the rarer zeolites.
Whewellite is a mineral, hydrated calcium oxalate, formula Ca C2O4·H2O. Because of its organic content it is thought to have an indirect biological origin; this hypothesis is supported by its presence in coal and sedimentary nodules. However, it has also been found in hydrothermal deposits where a biological source appears improbable. For this reason, it may be classed as a true mineral.
Glauberite is a monoclinic sodium calcium sulfate mineral with the formula Na2Ca(SO4)2.
Howlite, a calcium borosilicate hydroxide (Ca2B5SiO9(OH)5), is a borate mineral found in evaporite deposits.
Strontium sulfide is the inorganic compound with the formula SrS. It is a white solid. The compound is an intermediate in the conversion of strontium sulfate, the main strontium ore called celestite, to other more useful compounds.
Rapidcreekite is a rare mineral with formula Ca2(SO4)(CO3)·4H2O. The mineral is white to colorless and occurs as groupings of acicular (needle-shaped) crystals. It was discovered in 1983 in northern Yukon, Canada, and described in 1986. Rapidcreekite is structurally and compositionally similar to gypsum.
Syngenite is an uncommon potassium calcium sulfate mineral with formula K2Ca(SO4)2·H2O. It forms as prismatic monoclinic crystals and as encrustations.
Brianyoungite is a secondary zinc carbonate mineral. The Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (IMA) classifies it as a carbonate with the formula Zn3(CO3)(OH)4, but sulfate groups SO4 also occupy the carbonate CO3 positions, in the ratio of about one sulfate to three carbonates, so other sources give the formula as Zn3(CO3,SO4)(OH)4, and Gaines et al. classify the mineral as a compound carbonate. It is similar in appearance to hydrozincite, another zinc carbonate. It was discovered in 1991 and designated IMA1991-053. In 1993 it was named "brianyoungite" after Brian Young (born 1947), a field geologist with the British Geological Survey, who provided the first specimens.
Earlandite, [Ca3(C6H5O7)2(H2O)2]·2H2O, is the mineral form of calcium citrate tetrahydrate. It was first reported in 1936 and named after the English microscopist and oceanographer Arthur Earland FRSE. Earlandite occurs as warty fine-grained nodules ca. 1 mm in size in bottom sediments of the Weddell Sea, off Antarctica. Its crystal symmetry was first assigned as orthorhombic, then as monoclinic, and finally as triclinic.
Peretaite is a sulfate of antimony and calcium. The mineral, Ca(SbO)4(SO4)2(OH)2 (2(H2O)), was named Peretaite for its locality. It was first discovered in an antimony-bearing vein at Pereta, Tuscany, Italy.
