About
Anhydrite also exists as a relic of the past in several traprock occurrences, where the Anydrite dissolves and leaves a hollow cast around its original form. Epimorphs of Quartz and Prehnite over Anhydrite frequently form at certain localities, with the original Anhydrite totally replaced or dissolved.
Anhydrite sometimes occurs in arid regions, forming from the dehydration of Gypsum. Fine but usually small crystals may come from the rock area above salt domes, where the domes absorb all underground water and prevent it from entering the structure of the Anhydrite, which would otherwise cause it to alter to Gypsum. Anhydrite specimens in a collection may also alter to Gypsum if kept in moist conditions over a prolonged period of time.
Crystal Forms & Aggregates
Other ID Marks
Complex Tests
Striking Features
Environment
Varieties
✓ common · ✗ uncommon
Uses
Noteworthy Localities
At Rio Grande Do Sul, Brazil, very large Quartz pseudomorphs after Anhydrite were found in long and flattened crystals. Some of the best Anhydrite on the mineral market is the light blue dense fibrous veins, some quite large in size, from the mines at Naica, Chihuahua, Mexico. In Canada, Anhydrite comes from Faraday in the Bancroft District, Hastings Co., Ontario.
In the U.S., Quartz, Amethyst and Prehnite pseudomorphs, as well as empty Anydrite casts, are plentiful at Paterson and Prospect Park, Passaic Co., New Jersey. Intact specimens, partially altered to white Gypsum, have also been found nearby at the Braen's in Haledon, Passaic Co., New Jersey. Other significant Anhydrite occurrences are Balmat, Essex Co., New York; Isle Royale, Houghton Co., Michigan; Ajo, Pima Co., Arizona; Bisbee, Cochise Co., Arizona; the Carlsbad District of Eddy Co., New Mexico; Death Valley, Inyo Co., California; and the salt domes of southern Louisiana.
Common Mineral Associations
Distinguishing Similar Minerals
Barite - Much heavier.
Photos
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