gypsum

gypsum

a colourless or white mineral sometimes tinted by impurities, found in beds as an evaporite. It is used in the manufacture of plaster of Paris, cement, paint, school chalk, glass, and fertilizer. Composition: hydrated calcium sulphate. Formula: CaSO₄.2H₂O. Crystal structure: monoclinic

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

gypsum

[′jip·səm]

(mineralogy)

CaSO₄·2H₂O A mineral, the commonest sulfate mineral; crystals are monoclinic, clear, white to gray, yellowish, or brownish in color, with well-developed cleavages; luster is subvitreous to pearly, hardness is 2 on Mohs scale, and specific gravity is 2.3; it is calcined at 190-200°C to produce plaster of paris.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

gypsum

A soft mineral consisting of a hydrated calcium sulfate from which gypsum plaster is made (by heating); colorless when pure; used as a retarder in portland cement.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

gypsum

in egg shaped form, brings good fortune. [Gem Symbolism: Kunz, 80]

See: Luck, Good

Allusions—Cultural, Literary, Biblical, and Historical: A Thematic Dictionary. Copyright 2008 The Gale Group, Inc. All rights reserved.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Gypsum

 

a mineral, hydrous calcium sulfate CaSO₄ · 2H₂O; when pure it contains 32.56 percent CaO, 46.51 percent SO₃, and 20.93 percent H₂O.

Gypsum crystallizes in the monoclinic system. The crystal lattice structure of gypsum is of the layer type. Double layers consist of tetrahedra (SO₄) joined through calcium. Crystals are tabular, acicular (single or twinned, so-called swallow-tailed), needle-shaped, and fibrous. Gypsum is found mainly as continuous granular (alabaster) and fibrous (selenite) masses and as various crystal groups (such as gypsum rosettes). Pure gypsum is colorless and transparent; if impurities are present, it can be gray, yellowish, pinkish, brown, or other colors. The mineralogical-scale hardness is 1.5, density 2,300 kg/m³, and solubility 2.05 g per liter at 20° C (maximum between 32° and 41° C). It is precipitated from aqueous solutions rich in sulfates (in the drying up of marine lagoons and salt lakes). Gypsum is precipitated at relatively low salinity; when the salinity is raised, anhydrous calcium sulfate, or anhydrite, starts developing instead, followed by salts. Because of this effect, gypsum is often found with anhydrite, more rarely with halite and other salts. Many deposits were formed through hydration of anhydrite. The main gypsum formations are of the sedimentary type and are widely distributed in deposits of varying age. In the USSR the largest deposits occur in the Donbas and in Moscow, Kuibyshev, and Perm oblasts, as well as in the Caucasus and Middle Asia. Gypsum is widely used to make cementing materials, gypsum concrete, and articles made from gypsum and gypsum concrete; as sundry-purpose stone (selenite) and lining or facing stone; in making paints, enamels, and glazes; for gypsuming of the soil; and in medicine and optics.

Gypsum is used as the starting material in solutions for making hollow molds from a sculptured original, these molds serving for casting copies from bronze, porcelain, or other materials or from gypsum (details of modeled architectural decoration). Gypsum enters into the composition of ganch (a gypsum-clay mixture) and stucco, and stands up well to assembling and coloring.

REFERENCE

Budnikov, P. P. Gips, ego issledovanie i primenenie, 3rd ed. Moscow-Leningrad, 1943.

V. P. PETROV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.