Anhydrite

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Egyptian ointment jar
MFA# 65.1749

Description

A naturally occurring mineral of anhydrous calcium sulfate that is often found in gypsum deposits. Anhydrite was first identified as a mineral in deposits at Innsbruck, Austria in 1794. Other major deposits occur in Canada (Ontario), and the U.S. (Arizona, New Mexico). Anhydrite can be transparent or translucent and has a lustrous sheen. It occurs in several colors such as white, gray, blue, pink, red, and lavender. Anhydrite was used in ancient Egypt for carved objects and vessels, many of which are in the shape of animals (Fay, 1998). Powdered anhydrite has also been found as a filler in the gesso grosso ground layers of Italian paintings and polychromed sculpture. Currently, the colorless, inert pigment is often used as a filler in paper, paints, and plastics.

Anhydrite

Synonyms and Related Terms

anhydrous calcium sulfate; Anhydrit (Deut.); anhydrite (Fr.); anhidrita (Esp.); anydritis (Gr.); anidrite (It.); anhydriet (Ned.); anhydryt (Pol.); anidrite (Port.); blue marble; anhydrite white;

FTIR (PMA)

Anhydrite PMA.TIF

Raman

AnhydriteRS.jpg

Chemical structure

Anhydrite.jpg


Risks

  • Can alter to gypsum in humid conditions.
  • USG: SDS

Physical and Chemical Properties

  • Orthorhombic crystals but usually massive.
  • Perfect cleavage in three directions.
  • Sometimes fluorescent, especially after heating.
  • Fracture = uneven.
  • Luster = vitreous to pearly.
  • Streak = white to gray.
  • Under cross polars, particles usually show bright second order interference
Composition CaSO4
CAS 7778-18-9
Mohs Hardness 3.0 - 3.5
Melting Point 1450 C
Density 2.9-3.0 g/ml
Molecular Weight 136.14
Refractive Index 1.570; 1.575; 1.614

Additional Images

Resources and Citations

  • B.Fay ""Egyptian Duck Flasks of Blue Anhydrite" in Metropolitan Museum Journal, 33:23-48, 1998.
  • Nicholas Eastaugh, Valentine Walsh, Tracey Chaplin, Ruth Siddall, Pigment Compendium, Elsevier Butterworth-Heinemann, Oxford, 2004 Comment: Refractive Index: alpha=1.569-1.574; beta=1.574-1.579; gamma=1.609-1.618
  • R. J. Gettens, G.L. Stout, Painting Materials, A Short Encyclopaedia, Dover Publications, New York, 1966 Comment: density = 2.93; refractive index = 1.570; 1.614; 1.575
  • C.W.Chesterman, K.E.Lowe, Audubon Society Field Guide to North American Rocks and Minerals, Alfred A. Knopf, New York, 1979
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 38
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983