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Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as far back as the Archaean eon. [16] Gypsum is deposited from lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins.
Selenite, satin spar, desert rose, and gypsum flower are crystal habit varieties of the mineral gypsum.. All varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate (meaning that it has two molecules of water), with the chemical formula CaSO 4 ·2H 2 O. Selenite contains no selenium, the similar names both derive from Greek selḗnē (σελήνη 'Moon').
Black alabaster is a rare anhydrite form of the gypsum-based mineral. The black form is found in only three veins in the world, one each in United States, Italy, and China. Alabaster Caverns State Park, near Freedom, Oklahoma, is home to a natural gypsum cave in which much of the gypsum is in the form of alabaster. There are several types of ...
An ancient Roman grave filled with white gypsum was found in England, officials announced last week. ... "a rare find." ... The coffin was so heavy in part because it was filled with a substance ...
The oxygen slowly diffused into the heated water and oxidized the sulfides (S 2−) into sulfates (SO 2− 4 ) that precipitated as anhydrite (CaSO 4 ). When the overall temperature of the cave started to drop below 56 °C (133 °F), the hydrothermal and sedimentary anhydrite crystals dissolved, and gypsum (CaSO 4 · 2 H 2 O ) crystals formed ...
The gypsum is mostly in the form of alabaster. There are several types of alabaster found at the site, including pink, white, and the rare black alabaster. This black alabaster can be found in only three veins in the world, one each in Oklahoma, Italy and China. Another form of gypsum can be found in the many selenite crystal formations. [4]
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These rare compounds contain organic carbon, but can be formed by a geologic process. For example, whewellite , CaC 2 O 4 ⋅H 2 O is an oxalate that can be deposited in hydrothermal ore veins. While hydrated calcium oxalate can be found in coal seams and other sedimentary deposits involving organic matter, the hydrothermal occurrence is not ...