Anhydrite - Encyclopedia

    Class : Sulphates, chromates, molybdates
    Subclass : Anhydrous sulfates
    Crystal System : Orthorhombic
    Chemistry : CaSO4
    Rarity : Very common

Anhydrite is a common mineral in sedimentary evaporitic deposits : it precipitates directly from seawater in a lagoon environment as soon as the temperature reaches 42°C, thus constituting thick layers, associated with gypsum or halite. Still in an evaporitic context, anhydrite is common in large clusters in the sulphur cap-rocks that cap the salt domes of Texas, Louisiana and Germany. It is also a hydrothermal alteration mineral of limestone and dolomitic rock, exceptionally a matrix mineral from hydrothermal veins (Balmat, New York). By hydration, it is transformed into gypsum with an increase in volume ; it is nevertheless much less frequent than the latter. Its name comes from the Greek anhudôr (without water) as opposed to gypsum which is hydrated. Its crystals are rare, tabular or prismatic, frequently flattened. Anhydrite occurs mainly in large crystalline masses showing three perpendicular cleavages between them, simulating a cubic system. It is rarely fibrous (parallel fibers, radiating and often curved), or in concretions. Anhydrite is white or grayish, often tinged with gray-blue or purple, more rarely reddish, brownish, or a magnificent pink-mauve. Anhydrite is used for acid soil amendment and sometimes as a set retarder in some cements. It has also been used as a source of sulfur and for the production of sulfuric acid in England and Germany, but this use remains marginal. Particularly aesthetic specimens of anhydrite are sometimes cut in cabochon for jewelry or carved, this is particularly the case of the famous angelite, a massive Peruvian blue variety.

Anhydrite from Naica, Chihuahua, Mexico - © Rob Lavinsky
Anhydrite from Stassfurt, Germany - © Rock Currier
52,00 ct angelite cabochon from Peru
Anhydrite from Campiano Mine, Italy - © Enrico Bonacina

Anhydrite in the World

Fine samples of anhydrite are rare. Extraordinary tabular crystals of a strong mauve, reaching 10 cm, were discovered during the drilling of the Simplon tunnel (Switzerland), in the fissures of the Alpine Triassic. The Austrian (Hallein, Bad Aussee, Hall), Swiss (Bex) and German (Douglas-Hall, Stassfurt) evaporitic deposits also yielded colorless to reddish centimetric crystals. The Mexican deposit of Naica (Chihuahua), and South Africa of Nababeep yielded malformed white to bluish crystals of 10 cm.

Main photo : Anhydrite from Naica, Chihuahua, Mexico - © Rob Lavinsky

Anhydrite in France

In France, anhydrite is common in the South-West saliferous Triassic (Dax, St-Pandelon) where it constitutes cleavable masses and rare crystals.


Anhydrite presents twin on {011} as contact twins and polysynthetic lamellae as well as on {120} as a contact twin (rare).

Fakes and treatments

No fake reported for this species.

Hardness : 3 to 3.5
Density : 2.98
Fracture : Irregular
Trace : White

TP : Translucent to transparent
RI : 1.567 to 1.618
Birefringence : 0.042 to 0.044
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : Blue, red

Solubility : Acids

Magnetism : None
Radioactivity : None


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