Another
rose-red massive stone is furnished by the variety of zoisite known as
thulite. This resembles rhodonite in color somewhat, but is easily
distinguished by its chemical characters, zoisite being a hydrous
silicate of calcium and aluminum. It is somewhat harder than
rhodonite, its hardness being 6-6.5. The name thulite is from Thule,
an ancient town of Norway, and the occurrence of thulite is confined
almost exclusively to that country. Its use for ornamental purposes is
very limited; but it answers well where objects of its particular color
are desired.
PRECIOUS SERPENTINE
This
mineral resembles jade in appearance and properties, and is suited to
many of the ornamental uses to which the former is put. Not a little
so-called jade is doubtless serpentine. The hardness of serpentine is
somewhat below that of jade, it being 5.5, and lower. It is also
lighter, its specific gravity being 2.50-2.65. The blowpipe and
chemical characters also distinguish it, serpentine being practically
infusible before the blowpipe, and decomposed by acids, while jade is
more or less fusible, and not attacked by acids. In composition
serpentine is a hydrous magnesium silicate having the percentages,
silica 44.1, magnesia 43.0, and water 12.9. Like jade it does not
crystallize, but occurs in massive forms, which show crystalline
structure. One of the most pleasing properties of serpentine is its
luster, which is subresinous to oily. This, coupled with translucency
which characterizes most precious serpentine, and the excellent polish
which it takes, make the stone of rich effect.
The
color of precious serpentine is primarily some shade of green, varying
from yellowish-green to blackish-green. This color may be uniform or
mottled, or may include spots of other minerals, such as the white of
calcite, as in several of the serpentine marbles, or cherry-red from
iron oxide, as in the serpentine of Lizard, England. The name
serpentine alludes to the green, serpent-like cloudings best seen in
serpentine marble.
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