Gypsum is one of the most abundant minerals and is found especially in evaporite environments. Alabaster, the massive, granular variety, has been used for thousands of years, made into vases, bowls, and other useful and decorative objects. Today it is used in ashtrays, clock housings, paperweights, and so forth.
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|Varieties||Alabaster, Satin Spar, Selenite|
|Alternate Common Names||Also known as Alabaster, a variety of Satin Spar|
|Crystallography||Monoclinic. Crystals often perfect and large; tabular; rosettes; lenticular; helictites are grotesque shapes found in caves; often twinned; massive; granular.|
|Colors||Colorless, white, gray; impurities make it yellowish, reddish, brownish, greenish. Sometimes banded and patterned like marble.|
|Luster||Subvitreous; pearly on cleavages.|
|Polish Luster||Waxy to subvitreous|
|Fracture Luster||Dull to pearly|
|Density||2.32 (range 2.30-2.33)|
|Cleavage||Perfect and easy, I direction; distinct 2 other directions.|
|Stone Sizes||Massive gypsum in any desired size (for cabochons and carvings). Fibrous material cut into large carvings, up to several pounds. Faceted gypsum could be up to hundreds of carats, as large transparent crystals exist.|
|Luminescence||Sometimes indistinct brownish or greenish white in UV. Inert in X-rays.|
|Enhancements||Dyeing, common. Bleaching, common. Occasional heating to improve color, prepare for dying.|
|Transparency||Translucent to Opaque|
|UV Long||Inert to weak brownish to greenish white|
|UV Short||Inert to weak brownish to greenish white|
|Absorption Spectrum||Not diagnostic|
Optics: a = 1.520; β= 1.523; γ= 1.530.
Biaxial (+), 2V= 58°.
Occurrence: In sedimentary rocks and deposits; saline lakes; oxidized parts of ore deposits; volcanic deposits. Utah; Michigan; Colorado; South Dakota; New Mexico; New York; Kansas; other states.
California: many locations.
Mexico: at Naica, Chihuahua, in enormous crystals to 6 feet long.
Braden, Chile: crystals reported up to 10 feet long. Alabaster from England; Tuscany, Italy
Comments: Gypsum is one of the most abundant minerals and is found especially in evaporite environments. Alabaster, the massive, granular variety, has been used for thousands of years, made into vases, bowls, and other useful and decorative objects. Today it is used in ashtrays, clock housings, paperweights, and so forth.
Gypsum can be scratched by the fingernail, so it is much too soft for hard use. Care must be taken in handling carvings and useful objects, but scratches can be polished out rather easily.
Selenite is the term applied to colorless, transparent crystals. Satin spar is used to describe massive fibrous varieties that are often cut into cabochons or carved into animal shapes. This material has a great chatoyancy, and brown-colored satin spar makes lovely decorative items. Faceted gypsum is not often seen since cut stones are unattractive and very difficult to fashion, due to the exceptionally perfect cleavage and low hardness of the material.
Name: Gypsum from the Greek gypsos, a name applied to what we now call plaster. Satin spar in allusion to the satiny luster of the fibrous material. Selenite from the Greek word for moon, due to the pearly luster on cleavage surfaces. Alabaster f tom the Greek word alabastros, a stone from which ointment vases were made.
Variety Names: Also known as Alabaster. Selenite transparent, colorless gypsum.
Trade Names: Satinspar fibrous gypsum.