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Onyx & Turquoise
Onyx is a banded variety of
chalcedony, a cryptocrystalline form of
quartz.
The colors of its bands are white and black. Sardonyx is a variant, where the colored bands are
sard, rather
than black.It is usually cut as a
cabochon,
or into beads, and is also used for
intaglios and
cameos,
where the bands make the image contrast with the ground. Some onyx is
natural but much is produced by the staining of
agate.
Culture and historical/mythical usage
According to
Rebbenu Bachya, the word "Shoham" in the verse
Exodus
28:20 means "Onyx" and was the stone on the
Ephod
representing the tribe of
Joseph.
There were also two Shoham stones on the shoulders of the Ephod.
Turquoise (or turquois) is opaque, blue-to-green
hydrated
copper
aluminium
phosphate
mineral
according to the
chemical formula CuAl6(PO4)4(OH)8·5H2O.
It is rare and valuable in finer grades and has been enjoyed as a
gem
and
ornamental stone for thousands of years owing to its unique hue. In
recent times turquoise—like most other opaque gems—has had its popularity
undermined by the introduction of treatments, imitations, and
synthetics onto the market, some difficult to detect even by experts.The word turquoise is very old and likely is derived from the
French pierre turquoise, meaning Turkish stone. This is
thought to have arisen from a misconception: turquoise does not occur in
Turkey
but was traded there, and the gem became associated with the country in
the West.
This article is licensed under the "GNU Free Documentation License". It uses material from the Wikipedia articles "Onyx",Turquoise".
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