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Gypsum


An important construction material that has been used for thousands of years



What is Gypsum?



Gypsum is an evaporite mineral most commonly found in layered sedimentary deposits in association with halite, anhydrite, sulfur, calcite and dolomite. Gypsum (CaSO4.2H2O) is very similar to Anhydrite (CaSO4). The chemical difference is that gypsum contains two waters and anhydrite is without water. Gypsum is the most common sulfate mineral.


Physical Properties of Gypsum

Chemical Classification sulfate
Color clear, colorless, white, gray, yellow, red, brown
Streak white
Luster vitreous, silky, sugary
Diaphaneity transparent to translucent
Cleavage perfect
Mohs Hardness 2
Specific Gravity 2.3
Diagnostic Properties cleavage, specific gravity, low hardness
Chemical Composition hydrous calcium sulfate, CaSO4.2H2O
Crystal System monoclinic
Uses Use to manufacture dry wall, plaster, joint compound. An agricultural soil treatment.


Uses of Gypsum?



Gypsum uses include: manufacture of wallboard, cement, plaster of Paris, soil conditioning, a hardening retarder in Portland cement. Varieties of gypsum known as "satin spar" and "alabaster" are used for a variety of ornamental purposes, however their low hardness limits their durability.


Gypsum from Michigan
Gypsum from Grand Rapids, Michigan. Specimen is approximately 4 inches (10 centimeters) across.


Gypsum from virginia
Gypsum from North Holston, Virginia. Specimen is approximately 1-1/2 inches (3.8 centimeters) across.


Satin spar Gypsum
Satin spar, a fibrous variety of gypsum from Derbyshire, England. Specimen is approximately 3 inches (7.6 centimeters) across.


Alabaster Gypsum
Alabaster, a variety of gypsum, from Pomaia, Italy. Specimen is approximately 3 inches (7.6 centimeters) across.


Gypsum translucency
The translucent characteristic of alabaster, a variety of gypsum, from Pomaia, Italy. Specimen is approximately 3 inches (7.6 centimeters) across.



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 Gypsum
Satin spar, a fibrous variety of gypsum from Derbyshire, England. Specimen is approximately 4 inches (10 centimeters) across.




gypsum wallboard and plaster
Wallboard and construction plaster are the primary industrial uses of gypsum in the United States.Photo © George Peters and iStockphoto.


Alabaster gypsum jar
Jar made of beautiful translucent alabaster gypsum by David MacFarlane, photo © David MacFarlane and iStockphoto.


Selenite Gypsum
Selenite, a variety of gypsum from Penfield, New York. Specimen is approximately 2-1/2 inches (6.4 centimeters) across.


Gypsum from New York
Selenite, a variety of gypsum from Penfield, New York. Specimen is approximately 2-1/2 inches (6.4 centimeters) across.


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