68 GEMS AND PRECIOUS STONES.
GEM-STONES OF LESSER VALUE.
There
are several mineral specimens, besides those mentioned in the previous
pages, that have been at one time or another used for ornamental
purposes, or for personal adornment, and although these cannot perhaps
claim to be strictly precious stones, yet, their consideration cannot
well be left out when dealing with gem-stones of a purely ornamental
character.
Moonstone.
Taking
the feldspar group we find that many of its varieties are used for
ornamental purposes, the best known being the moonstone ; this is the
opalescent variety named adularia, belonging to the orfhoelase—feldspar
section. The members of this group belong to the monoclone system (it
will he unnecessary to describe this system here, as it is in gems of
little importance. It however somewhat resembles the rhombic forms,
except that one axis is inclined and not at right angles to the other
two axes), and are silicates of alumina and potash; they have a
hardness of 6, and a specific gravity of 239-2G3, are almost infusible,
and are not acted upon by acids. The characteristic physical property
of the moonstone is, however, the peculiar chatoyant reflection
somewhat resembling that of the cat's-eye, only of a pearly-white colour, and is very marked when the stones are cut en caboclion.
The best moonstones come from Ceylon, and are cut in
large quantities there. They are not of much value now, although at one
time the moonstone was in great request, being " in the fashion." The
ancients employed this stone, and used it largely, although it is
doubtful whether the feldspar variety is always meant, when the
moonstone is referred to in their writings. The name hecatolite was
given to this stone, because it was thought to enclose the image of
Luna, one of the forms of the threefold goddess Hecate. The moonstone
of Dioscorides was probably crystallized gypsum or selenite.
Sunstone.
The
sunstone is also a member of this group, and is a spangled adularia,
containing minute micaceous scales. It is a reddish or golden coloured
stone, much darker than the moonstone. It is rarely used in jewellery
Avanturine Feldspar.
The avanturine feldspar contains minute particles of specular or titanic iron, or limonite, disseminated throughout its mass.
Amazon Stone.
Another
variety of the orthoclase feldspar occasionally used for ornamental
purposes, is the beautiful green mineral called Amazon stone, so named
because it was thought to come from the basin of the Amazon, in South
America. It used to be obtained from Siberia, but some beautiful
specimens have been lately obtained at Pike's Peak, Colorado, in
America. The colour is supposed to be due to minute traces of copper,
although this has been disputed. Some varieties of amazonite have a
spangled appearance, forming a green avanturine in fact.
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