Satin spar, less commonly atlas spar, is a trivial, partly obsolete name for fibrous varieties of the minerals gypsum, calcite,Krivovichev V. G. Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0. (in Russian) and aragonite. Satin spars have a characteristic satin (silky) luster. Despite their very low hardness (2 or 3 on the Mohs scale), satin spars are widely used as ornamental stones.
Spar is a general term for glassy, transparent to translucent minerals that cleave easily. Satin spars are not related to other minerals containing spar in their names, such as feldspar and fluorspar.
Main minerals and varieties Satin spar gypsum is a white, fibrous variety of gypsumR. A. Lidin, L. L. Andreeva, V. A. Molochko. Constants of inorganic substances: handbook. 3rd ed., reprinted, edited by R. A. Lidin. — Москва: Дрофа, 2008 г. — 685 с. (in Russian) that is sometimes called selenite. Satin spar calcite, or calcite spar, is a fibrous variety of calciteG. F. Herbert Smith. Gemstones. 14th ed., reviewed by F. C. Phillips. — London, Chapman & Hall, 1972. — 580 p. ISBN 0412108909 that superficially resembles satin spar gypsum (selenite),Boris Cantor. Collecting Minerals. 2nd edition, revised and enlarged. — Moscow: Nedra, 1991. — 173 p. (in Russian) but is much less common in nature. Aragonite is one of the polymorphic varieties of calcite, sometimes having the same satin effect.
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See also Azure spar Moonstone Belomorite Albite Tiger's eye
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