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PRECIOUS STONES 147.
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OBSIDIAN
Is a volcanic glass found in all volcanic regions.
It is amorphous.
Hardness, 5 to 5.5, and brittle; specific gravity, 2.3 to 2.6.
Lustre vitreous to metallic; takes a high polish; translucent to opaque, sometimes transparent.
It is not easily attacked by acids, but melts under the blowpipe.
Color,
bottle- and peridot-green, yellow, blue, white, velvet-black to gray
and brown. A streaked brown American variety is called mahogany
obsidian. Many specimens have black or yellow spots or veins.
Globular
masses of pearl-gray translucent obsidian, known as " obsidian bombs,"
or " marekanite," after a locality in Siberia, are found occasionally
in Siberia and Western Australia. These sometimes explode when struck;
hence the name.
Obsidian was used by primitive people for arrow-heads, knives, and other cutting implements.
Although
some specimens show very beautiful color and polish, it does not find
favor as a jewel, for the reason that it is practically the same as the
manufactured imitations of more precious stones.
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