How is gypsum different from anhydrite?

Calcium oxide (CaO) 41,2%, sulfur trioxide (S0₃) 58,8%. Isostructural with ferruchite; isostructural and isomorphic with α – BaSO₄ and α – SrSO₄. Crystal structure. Sulfur ions (S 6+ ) are located in the center of tetrahedral oxygen groups (O 2- ), and each calcium ion (Ca 2+ ) is surrounded by eight oxygen ions.

Materials

Crystals are rare; “Alpine-type” crystals are cubic in shape, others are prismatic, and in hydrothermal veins they are often tabular. Edges with strong striping. Continuous, coarse- and fine-grained, fibrous-radiant masses predominate. The cleavage is perfect; density 2,9 – 3; color colorless, cloudy white, bluish (to violet). Most of the impurities are only bituminous. Thermoluminescence and fluorescence under ultraviolet light were observed in some samples. It dissolves very poorly in water and does not decompose in hydrochloric acid. The powder dissolves in sulfuric acid. By adding water, it turns into gypsum.

Education and location

Distributed in sedimentary deposits of evaporite formation, in the roofs of salt domes. O forms at higher temperatures than gypsum. Possible formation as a result of the hydrothermal low-temperature process of mineral formation in vein and skarn deposits. Widely distributed as a rock-forming mineral, a frequent companion of gypsum in salt and dolomite deposits. It is deposited in drying up salt water bodies, for example, near Hannover, in the Southern Harz (Germany). Found in metamorphically transformed salt deposits; in the Simplon Pass tunnel (Switzerland); in the hydrothermal vein deposits of the Harz. Absorbing water, anhydrite turns into gypsum and increases in volume (by about 60%), forming anhydrite-gypsum layers with fine flattening.

Meaning and application

Named from the Greek. “anhydrous” (in relation to gypsum). Among other things, it is used for the production of ammonium sulfate, in the production of sulfuric acid and as a decorative stone in interior architecture. Anhydrite is used for decorative finishing of interior spaces; as an ornamental stone in jewelry; used in the cement industry; for the production of sulfuric acid. Similar minerals: Externally similar to calcite (different effect of HCl), gypsum (softer).

Properties of the Mineral

Color	Grey, white, pale blue, cobalt blue, purple, pale red.
Line color	white, gray-white
Origin of the name	from the Greek an – to deny and hydor – water, which indicates the absence of water in the composition of anhydrite, unlike gypsum.
Opening place	Salt mine, Hall valley, Hall, Innsbruck, Inn valley, North Tyrol, Tyrol, Austria
Opening year	1804
IMA status	valid
Chemical formula	CaSO4
Brilliance	glass fatty pearl
Transparency	transparent translucent turbid
Cleavage	perfect by perfect by average for
Kink	stepped
Hardness	3 3,5 4
Thermal properties	Transforms into α-CaSO4 at t = 1193°C. Melting point = ~ 1450°C.
Typical impurities	Sr,Ba,H2O
Strunz (8th edition)	6/A.08-50
Hey’s CIM Ref.	25.4.1
Dana (8th edition)	28.3.2.1
Molecular weight	136.14
Cell Options	a = 6.245(1) Å, b = 6.995(2) Å, c = 6.993(2) Å
Attitude	a:b:c = 0.893 : 1 : 1
Number of formula units (Z)	4
Unit cell volume	V 305.48 ų
Twinning	1) Contact twins fused together and polysynthetic lamellas (can be obtained by heating or pressure); 2) Fusion twins are known, but rare.
Point group	mmm (2/m 2/m 2/m) – Dipyramidal
Density (calculated)	2.95
Density (measured)	2.98
Pleochroism	visible, colorless to violet
Optical axis dispersion	strong r

ANHYDRITE – (1) mineral, calcium sulfate; (2) synonymous with the term anhydrite rock (a rock composed primarily of anhydrite). English name: Anhydrite
Other names (synonyms): Symbolic designation of anhydrite – Anh First isolated and described: The mineral anhydrite was described by Ludwig CF (1804) in his “Handbook of Mineralogy according to A.G. Werner.”
The International Mineralogical Association (IMA) considers Austria to be the country where anhydrite was first found. Origin of the name: Anhydrite is named from the Greek words “without water,” which indicates the difference in its composition from gypsum. New products with Anhydrite in the product catalog Products containing Anhydrite are presented in the following categories:

• Unique exhibits and interior items,
• Stones and minerals,
• Products and souvenirs,
• Stone beads

• class Sulfates (selenates, tellurites, chromates, molybdates, tungstates)
  • subclass Sulfates (selenates, etc.)
    • mineral anhydrite
      • Angelite variety

      Allomorphite (allomorphite) – pseudomorphosis of barite after anhydrite (Krivovichev V.G., 2008, p. 18 and mindat.org)
      Anhydritegypsum (anhydrite gypsum) – a mixture of anhydrite and gypsum (Krivovichev V.G., 2008, p. 27); anhydrous gypsum – synonym for anhydrite (mindat.org)
      Angelite (angelite) – the local name for blue anhydrite nodules in Peru, diameter up to 12 cm, used as an ornamental stone (Bukanov V.V., 2008, p. 260); cm. angelite
      Anhydrite rock – a rock consisting mainly of anhydrite (VSEGEI Geological Dictionary); anhydrite-stone – sedimentary rock consisting mainly of anhydrite (mindat.org)
      Anhydritolite = Anhydrite rock (VSEGEI Geological Dictionary)
      Angelite (angelite) – anhydrite (Krivovichev V.G., 2008, p.27); the trade name of a bluish-gray translucent fine-grained variety of anhydrite, positioned on the market as jewelry raw materials, a local material for stone-cutting products in Lima (Peru), balls, eggs, magic wands are made from it, animal figures are carved, magical powers are attributed to the stone (mindat.org ); cm. angelite
      Anidrite (anidrite) – anhydrite (Krivovichev V.G., 2008, p. 28); Italian name for anhydrite (mindat.org)
      Bardiglionite (bardiglionite) – anhydrite (Krivovichev V.G., 2008, p. 45); bardiglione – Italian synonym for anhydrite (mindat.org)
      Bergamasco marble (bergamas marble) – anhydrite (Krivovichev V.G., 2008, p. 53); same as vulpinitis (Great Soviet Encyclopedia, 1969-1986)
      Fibrous anhydride (faseranhydrit) – anhydrite (Krivovichev V.G., 2008, p.84)
      Vulpinitis (vulpinite) – anhydrite (Krivovichev V.G., 2008, p. 86); a granular variety of anhydrite, first discovered at Costa Volpino, Italy (mindat.org); blue fine-grained anhydrite (Great Soviet Encyclopedia, 1969-1986); the name of dense colored anhydrite aggregates in Italy (Bukanov V.V., 2008, p.260)
      Ythtromicrolite (yttromicrolite) – a mixture of anhydrite (?), tantalite-(Fe) and microlite (Krivovichev V.G., 2008, p. 146); the name of a discredited mineral that turned out to be an amorphous mixture of calcium sulfate, tantalite and heterogeneous microlite (mindat.org)
      Kalkbarite (calcbaryte, kalcbaryte) – a mixture of barite and anhydrite (Krivovichev V.G., 2008, p. 151)
      Karstenite (karstenite) – anhydrite (Krivovichev V.G., 2008, p. 160); synonym of anhydrite (mindat.org)
      Bone plaster (bony gypsum) – anhydrite (Krivovichev V.G., 2008, p. 179)
      Bone spar (bone spar) – anhydrite (Krivovichev V.G., 2008, p. 179)
      Krugit (krugite) – a mixture of polyhalite and anhydrite (Krivovichev V.G., 2008, p. 183 and mindat.org)
      Cubic anhydrite (cubic anhydrite) – anhydrite (Krivovichev V.G., 2008, p. 185) [probably a type of pseudocubic anhydrite]Cubic spar (cube spar) – anhydrite (Krivovichev V.G., 2008, p. 185); synonym of anhydrite (mindat.org) [probably a pseudocubic type of anhydrite]curly stone (curly stone) – (1) anhydrite (Krivovichev V.G., 2008, p. 189); (2) curlstone (English-Russian Geological Dictionary, 1988, p. 118); (3) shale, belonging to a coal formation, which, when exposed to air, hardens into a peculiar shape, sometimes called “cone-to-cone,” also called curlstone (mindat.org) [curlstone is an ironstone with a “cone-to-cone” structure (Petrographic Dictionary , 1963)]Leedsit (leedsite) – a mixture of anhydrite and barite (Krivovichev V.G., 2008, p. 195 and mindat.org)
      Muriacite (muriacite) – anhydrite or halite (Krivovichev V.G., 2008, p. 238); synonym of anhydrite, formerly also known as halite (mindat.org)
      Calcium sulphate (calcium sulfate) – anhydrite (Krivovichev V.G., 2008, p. 329); anhydrous sulfate of lime – synonym for anhydrite (mindat.org)
      Tripod stone (gekrösestein) – anhydrite (Krivovichev V.G., 2008, p. 347); gekrösstein – German synonym for anhydrite (mindat.org); bowel stone – a type of anhydrite, with folds (specific formation) resembling intestines (mindat.org)