Specific gravity: 2.98
Hardness: 3 to 3½
Colour: Colourless, white, grey, blue
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Evaporite Deposits (typical)
Anhydrite occurs in chemical sedimentary deposits and in the oxidation zone of high temperature hydrothermal
replacement deposits. It is found in
limestone and in some
amygdaloidal cavities in basalt.
It is a common alteration mineral in some porphyry (rock with coarse phenocrysts in a finer groundmass)
copper deposits, particularly those associated with diorite and
granodiorite intrusions. Gypsum
is a common associate
In carbonatites it is associated with baryte and gypsum (AS).
At Maricopa, Arizona, USA, quartz pseudomorphs after anhydrite have been found (KL p245).
At the Upper New Street quarry, Paterson, Passaic county, New Jersey, USA, a datolite pseudomorph after anhydrite has been found, with dozens of datolite crystals forming a flat cast where a blade of anhydrite once existed, but has since dissolved away. Prehnite pseudomorphs after anhydrite are also found here (KL p223, 241).
anhydrite and water to gypsum
Ca(SO4) + 2H2O ⇌ Ca(SO4).2H2O
Gypsum is frequently formed by the hydration of anhydrite.
Common impurities: Sr,Ba,H2O
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