GYPSUM - An important construction material that has been used for thousands of years - 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. 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. 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 Used to manufacture dry wall, plaster, joint compound. An agricultural soil treatment. Gypsum wallboard and plaster: Wallboard and construction plaster are the primary industrial uses of gypsum in the United States.

 

Gypsum

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

Article by: Hobart M. King, PhD, RPG

 

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.

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.

 

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	Used to manufacture dry wall, plaster, joint compound. An agricultural soil treatment.

 

Hobart M. King, Ph.D., GIA GG

Hobart M. King is the manager and publisher of Geology.com. He is a geologist with over 40 years of experience, has a Ph.D. in geology, and is a GIA graduate gemologist. Much of his work has focused on coal geology, industrial minerals, gemology, geologic hazards, and geoscience education.

He has authored many of the internet’s most popular articles about rocks, minerals and gems. He writes most of the content published on Geology.com and compiles its daily news. His writing is read by over a million people each month, making him one of the world’s most widely read geologists.

Dr. King earned a Ph.D. and an M.S. in geology from West Virginia University; a B.S. in geology from California University of Pennsylvania; and, a Graduate Gemologist Diploma from the Gemological Institute of America. He is a registered professional geologist in the Commonwealth of Pennsylvania.

He has worked as a geologist in a variety of settings since 1975.

https://geology.com/minerals/gypsum.shtml

 

 

 

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. 

 

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

 

Gypsum from Michigan: Gypsum from Grand Rapids, Michigan. Specimen is approximately 4 inches (10 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.

 

Alabaster gypsum jar: Jar made of beautiful translucent alabaster gypsum by David MacFarlane

 

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.

 

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.