Anhydrite
Current inventory:  0 gems
 

  
Anhydrite is named from the Greek word anhydros meaning without water, in allusion to the lack of water in its composition, in contrast to Gypsum, which contains water.

Discovered in 1795 (or 1804);   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

CaSO₄

Calcium Sulfate

Molecular Weight:

136.14 gm

Composition:

Calcium

29.44 %

Ca

41.19 %

CaO

Sulfur

23.55 %

S

58.81 %

SO₃

Oxygen

47.01 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Sulfates

Strunz 8th Ed. ID:

5/B.04-40

Nickel-Strunz 10th Ed. ID:

7.AD.30

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
A : Sulfates (selenates, etc.) without additional anions, without H₂O
D : With only large cations

Related to:

Dehydrated form of Gypsum. Isostructural with Ferruccite.

Members of Group:

n/a

Varieties:

Angelite, Bowel Stone, Vulpinite

Synonyms:

Anhydrous Gypsum, Anhydrous Sulfate of Lime, Cube Spar, Karstenite, Muriacite, Siliceous Anhydrous Gypsum

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals tabular on {010}, {100}, or {001} or equant with large pinacoidal faces; elongated along [100] or [001], to 15 cm, with about 40 forms recorded. Typically granular, nodular, parallel or divergent fibrous, massive. Contorted concretionary forms (Bowel Stone).

Twinning:

Simple or repeatedly on {011}, common; contact twins rare on {120}.

Physical Properties

Cleavage:

Perfect on {010}, nearly Perfect on {100}, Good to Imperfect on {001}; yielding pseudocubic fragments.

Fracture:

Irregular/Uneven, Spintery

Tenacity:

Brittle

Moh's Hardness:

3.0 - 3.5

Density:

2.96 - 2.98 (g/cm³)

Luminescence:

Occassionally red under LW UV

Radioactivity:

Not Radioactive

Optical Properties

Color:

Colorless, White, pale Blue, pale Violet, Mauve, Rose, pale Brown or dark Gray from included impurities. Colorless in transmitted light.

Transparency:

Transparent to Translucent

Luster:

Pearly on {010}, Vitreous to Greasy on {001}; Vitreous on {100}.

Refractive Index:

1.567 - 1.618  Biaxial ( + )

Birefringence:

0.0420 - 0.0440

Dispersion:

Strong; r < v

Pleochroism:

Visible. Violet coloured material: X = colourless to very light yellow or rose; Y = light violet or rose; Z = violet.

Occurances

Geological Setting:

A major component in sedimentary evaporite deposits and in the cap rocks above salt domes, commonly formed by dehydration of gypsum; in igneous rocks, fumarolic deposits, and in seafloor hydrothermal chimneys, also an alteration product in hydrothermal mineral deposits.

Common Associations:

Gypsum, Halite, Sylvite, Polyhalite, Dolomite, Calcite, Magnesite, Celestine, Sulfur

Common Impurities:

Sr, Ba, H2O

Type Locality:

Salt mine, Hall, Innsbruck, Inn valley, North Tyrol, Tyrol, Austria

Year Discovered:

1795 (or 1804)

View mineral photos:

Anhydrite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Anhydrite is a relatively common sedimentary mineral that is the result of dewatering of the rock forming mineral Gypsum (CaSO4 • 2H2O). Good crystal specimens of Anhydrite are extremely rare so faceted gems are also extremely rare. However, fine semi-translucent to opaque specimens of Anhydrite have been found in Mexico and Peru that have a fine blue color. This material is called Angelite for its "angelic" blue color.

Faceted gems, although extremely rare, are known from crystals found at Faraday Mine, Bancroft, Ontario, Canada; Leopoldshall, Stassfurt, Stassfurt Potash deposit, Saxony-Anhalt, Germany; and Simplon Railway Tunnel, Simplon Pass area, Brig, Wallis, Switzerland. These gems are pale purple and usually somewhat included. Blue Angelite is found at Naica, Mun. de Saucillo, Chihuahua, Mexico and Lima Department, Peru.
 

  
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