Satin spar

Satin spar, less commonly atlas spar, is a trivial, partly obsolete name for fibrous varieties of the minerals gypsum, calcite,^[1]: 40 and aragonite.^[2] 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.

Satin spar gypsum from England

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.^[3]

Main minerals and varieties

• Satin spar gypsum is a white, fibrous variety of gypsum^[4]: 217 that is sometimes called selenite.
• Satin spar calcite, or calcite spar, is a fibrous variety of calcite^[5]: 429 that superficially resembles satin spar gypsum (selenite),^[6]: 169 but is much less common in nature.
• Aragonite is one of the polymorphic varieties of calcite,^[5]: 429 sometimes having the same satin effect.

See also

• Azure spar
• Moonstone
• Belomorite
• Albite
• Tiger eye