(CALCITE, GYPSUM)
The term alabaster is derived from a kind of ointment vases called alabastra, which
the Egyptians and peoples of a later period were accustomed to carve
out of stone. This stone was largely a stalagmitic calcite obtained at
Thebes, but it is probable that gypsum was also used to some extent. At
the present time the term is used loosely for either of these minerals
when employed for the manufacture of ornamental objects, although
stalagmitic calcite is now more generally designated as onyx.
Both
calcite and gypsum are soft minerals, the hardness of the former being
3, and that of the latter 2. They are not therefore fitted to endure
wear, and can only be employed for objects such as vases, boxes,
statuary, etc., not likely to be subjected to much attrition. Both
stalagmitic calcite, however, and gypsum take an excellent polish, and
preserve it if properly cared for.
The
term alabaster when referred to gypsum is limited to the finegrained
granular variety usually white or delicately shaded. It is obtained
largely at Castelino, near Leghorn, in Italy, and is used for carvings
of various sorts. Objects are often sold under the names of alabaster
that have been made out of plaster of paris by molding. These can be
distinguished from true alabaster by their lack of translucency.
Another
form of gypsum used for ornamental purposes is that known as satin
spar. This is white, with a delicately fibrous structure, and exhibits
when polished a beautiful silky luster and pearly opalescence. Large
quantities of this cut in the form of necklaces, charms, etc., are
often sold at Niagara Falls and vicinity to tourists as made from
material found at the Falls. Although gypsum occurs there, it is not in
this form, and the material used in this way is really obtained in
Wales.
Objects
made from calcite can usually be detected by their softness, as they
scratch easily and deeply with a knife, and by their effervescing when
touched with a drop of any common acid. In the form of Mexican onyx
calcite is extensively used for ornamental purposes, and many locally
fashioned stones, such as the Petoskey, Michigan, fossil corals (often
called agates), and the Gibraltar stone, of Gibraltar, belong to this
mineral species.
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