Description
A soft, transparent, easily cleaved mineral composed of hydrated calcium sulfate. Gypsum is found as twinned monoclinic crystals, called selenite, or silky fibrous crystals, called satin spar. Massive blocks of fine-grain white, translucent gypsum are called alabaster and have been used since ancient times for carved ornamental objects and statuary. Gypsum is a commonly found mineral associated with sedimentary rock and deposits from seas, lakes, and volcanic springs (gypcrete). For a long time, gypsum quarries in the Montmartre district of Paris supplied the starting material for the burnt gypsum that was, and still is, called plaster of Paris. Raw gypsum is used for carvings (alabaster), for wallboards (Sheetrock®), as a filler in paper (crown filler), as a paint pigment (terra alba) and as an ingredient in portland cement. Finely ground gypsum was mixed with rabbit skin glue and used as gesso.
Synonyms and Related Terms
native calcium sulfate; alabaster; selenite; terra alba; satinite; mineral white; satin spar; light spar; sulfate of lime; puritan filler; crown filler; Pigment White 25; Gips (Deut.); gips (Ned., Pol.); yeso (Esp.); gypse (Fr.); gesso (It., Port.)
| CaSO4-2H2O |
| 1010-14-4 |
| 1.5 - 2.0 |
| 100-150 |
| mol. wt. = 172.2 |
| 2.32-2.36 |
| 1.520; 1.523; 1.530 |
Other Properties
Soluble in water. Slightly soluble in glycerol and weak acids. Precipitates as needle-like crystals. Insoluble in most organic solvents. Gypsum fluoresces purple.
Low birefringence. Perfect cleavage in one direction and good cleavage in two directions.
Luster = vitreous, silky or pearly. Streak = white. Fracture = conchoidal to splintery. Euhedral shaped crystals contain numerous inclusions.
Hazards and Safety
Inhalation and contact may cause slight allergies.
LINK: International Chemical Safety Card
Additional Information
Mineralogy Database: Gypsum
|
Last updated on: 3/12/2010 7:58:05 AM
|
|
 |
|
