Alabaster is the stone of art par excellence, a much-appreciated resource for sculptors and architects who, from antiquity until these days, have been able to take advantage of its characteristic features, above all the ease with which it can be worked and polished and its translucency, a property as rare among rocks as effective in magnifying their natural beauty.
“Alabastron” was the name of a village in Old Egypt, located near the city of Thebes, in which a calcareous-type translucent stone was extracted. It seems that the term also referred to objects (e.g. vessels, cups) originating from that place, which, originally, were made with this material. Eventually, the term began to refer only to the white translucent rock used in art and in the manufacturing of muchappreciated vessels.
Today, the term alabaster refers to a massive, competent, translucent gypsum variety, with very low porosity and displaying very light colours. It consists of microcrystalline gypsum aggregates, with sizes ranging from 10 to 80 micrometres, which form an irregular mosaic. Aggregates of finest grain size are the best quality and most translucent. Impurities among the aggregates, above all clays and other salts that could have accumulated with the gypsum, are common and can colour and pattern the set.
Alabaster under the microscope
Alabaster Boulder
ALABASTER MATERIAL COMPOSITION
The chemical composition of alabaster is the same as that of gypsum: i.e. dihydrate calcium sulphate: CaSO3*2H2O. Gypsum can become dehydrated and lose the water molecules in greater o smaller proportion. If it dehydrates completely, the new mineral is called anhydrite (calcium sulphate, CaSO3). Although gypsum is more stable under normal environmental conditions, it can coexist with anhydrite and, to a lesser extent, with bassanite.
When temperature or humidity is increased the composition of this substance can be altered. Indeed, the ease with which calcium sulphate becomes hydrated or dehydrated due to pressure, temperature and humidity conditions is decisive to alabaster genesis.
When alabaster is exposed to rainwater, it dissolves and grooves develop.
Alabaster exposed to rainwater
Source: Myriam Gonzalez Cavazos
Also you can have a look about how the alabaster is form.
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Images about alabaster projects in our Home Arastone page.
