Alabaster is a name applied to varieties of two distinct minerals, when used as a material: gypsum (a hydrous sulfate of calcium) and calcite, a carbonate of calcium, also known as onyx-marble, Egyptian alabaster or Oriental alabaster, in geological terms is ""a stalagmitic limestone marked with patterns of swirling bands of cream and brown"". In general, but not always, ancient Alabaster in Egypt and the Near & Middle East is calcite. Alabaster in medieval Europe is gypsum. Modern Alabaster is probably calcite, but may be either. Both are easy to 'work' and as both are slightly water-soluble, have been used for making a variety of indoor artworks and carvings, as they will not survive long outdoors.The two kinds are distinguished from each other readily by differences in their relative hardness. The gypsum kind is so soft as to be readily scratched with a fingernail (Mohs hardness 1.5 to 2), while the calcite kind is too hard to be scratched in this way (Mohs hardness 3), although it does yield readily to a knife. Moreover, the calcite alabaster, being a carbonate, effervesces upon being touched with hydrochloric acid, whereas the gypsum alabaster, when thus treated, remains practically unaffected.The characteristic color of white alabaster has lent its name as a common description of white things, particularly ""alabaster skin"", which means very light and quite translucent, and possibly derives from the use of alabaster for tomb effigies.