Alabaster is a mineral and a soft rock used for carvings and as a source of plaster powder. Archaeologists, geologists, and the stone industry have different definitions for the word alabaster. In archaeology, the term alabaster includes objects and artefacts made from two different minerals: (i) the fine-grained, massive type of gypsum,[1] and (ii) the fine-grained, banded type of calcite.[2]
Chemically, gypsum is a hydrous sulfate of calcium, whereas calcite is a carbonate of calcium.[2][3] As types of alabaster, gypsum and calcite have similar properties, such as light color, translucence, and soft stones that can be carved and sculpted; thus the historical use and application of alabaster for the production of carved, decorative artefacts and objets d’art.[3] Calcite alabaster also is known as: onyx-marble, Egyptian alabaster, and Oriental alabaster, which terms usually describe either a compact, banded travertine stone[2] or a stalagmitic limestone colored with swirling bands of cream and brown.[3]
In general, ancient alabaster is calcite in the wider Middle East, including Egypt and Mesopotamia, while it is gypsum in medieval Europe. Modern alabaster is most likely calcite but may be either. Both are easy to work and slightly soluble in water. They have been used for making a variety of indoor artwork and carving, as they will not survive long outdoors.
The two types are readily distinguished by their different hardness: gypsum alabaster (Mohs hardness 1.5 to 2) is so soft that a fingernail scratches it, while calcite (Mohs hardness 3) cannot be scratched in this way but yields to a knife. Moreover, calcite alabaster, being a carbonate, effervesces when treated with hydrochloric acid, while gypsum alabaster remains almost unaffected.[4]
- ^ "Gypsum". Britannica. Archived from the original on 8 January 2017. Retrieved 8 January 2017.
- ^ a b c More About Alabaster and Travertine: Brief Guide explains the different definitions used by geologists, archaeologists, and the stone trade. Oxford University Museum of Natural History, 2012, [1]
- ^ a b c "Grove": R. W. Sanderson and Francis Cheetham. "Alabaster", Grove Art Online, Oxford Art Online, Oxford University Press, accessed 13 March 2013, subscriber link.
- ^ One or more of the preceding sentences incorporates text from a publication now in the public domain: Rudler, Frederick William (1911). "Alabaster". In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. pp. 466–467. Endnotes:
- M. Carmichael, Report on the Volterra Alabaster Industry, Foreign Office, Miscellaneous Series, No. 352 (London, 1895)
- A. T. Metcalfe, "The Gypsum Deposits of Nottingham and Derbyshire," Transactions of the Federated Institution, vol. xii. (1896), p. 107
- J. G. Goodchild, "The Natural History of Gypsum," Proceedings of the Geologists' Association, vol. x. (1888), p. 425
- George P. Merrill, "The Onyx Marbles," Report of the U. S. National Museum for 1893, p. 539.
