PRECIOUS STONES. 289
compressed
when soft into flat pieces known as Spiller imitations; it then shows
several peculiarities, such as streaks, a sharp demarcation between
clear and cloudy portions, and microscopically the cavities show signs
of deformation.
Amber
is largely worked into beads, mouth-pieces for pipes and
cigarette-holders, walking stick knobs, and the like. Sometimes it is
cut and polished to mount in a brooch. It can be easily worked in a
lathe and can be rendered temporarily flexible by heat.
Celluloid
imitations (Ambre antique) show the sharp demarcation between clear and
cloudy parts as in pressed amber; the smell of camphor may be elicited
on rubbing. Celluloid is rather sectile.
Jet.
Jet
is a dense compact variety of coal, near Cannel Coal and Lignite. It
shows no microscopic vegetable structure, and for the purposes of
cutting it must be free from Iron Pyrites. It is a dense black in
colour, and opaque. When polished it has a brilliant lustre, but an
unpolished surface is glistening or even rather greasy in lustre. The
fracture is conchoidal. The specific gravity is 1'35 and the hardness 3
to 4. On heating it burns readily, with a sooty flame. It is found in
flat pieces in Liassic rocks at Robin Hood's Bay, near Whitby, in
England, and in other parts of East Yorkshire ; in France in the
province of Languedoc; in Asturia in Spain; in Hesse ; the Erzgeberg,
Bavaria, and other parts of Central Europe. In America fine material is
found in Colorado.
It is largely used for mourning ornaments and for the p.s.
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