Alabaster

Alabaster (sometimes called satin spar) is a name applied to varieties of two distinct minerals: gypsum (a hydrous sulfate of calcium) and the calcite (a carbonate of calcium). The former is the alabaster of the present day; the latter is generally the alabaster of the ancients.

Related Topics:
Mineral - Gypsum - Hydrous - Sulfate - Calcium - Calcite - Carbonate

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The two kinds are readily distinguished from each other by their relative hardnesses. The gypsum kind is so soft as to be readily scratched by a finger-nail (hardness 1.5 to 2), while the calcite kind is too hard to be scratched in this way (hardness 3), though it does yield readily to a knife. Moreover, the calcite alabaster, being a carbonate, effervesces on being touched with hydrochloric acid, whereas the gypsum alabaster, when so treated, remains practically unaffected.

Related Topics:
Hardness - Carbonate - Hydrochloric acid

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