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light.
The lighter red and yellowish shades are less desirable, stones of
these shades being known as " female " carnelians, while those of the
darker shades are known as " male" carnelians. The colors are due to
oxides of iron, and can sometimes be changed by heating. Thus, the
yellowish and brownish carnelians, being colored by iron hydroxide, can
be changed by heating to red, the water being driven off and iron oxide
left. The heating may be done in the sun, or by some other slow means.
Even olive-green stones are changed in India to red by this process.
The color may also be introduced artificially, by allowing the stones
to lie in a mixture of metallic iron and nitric acid, or of iron
sulphate for a while. In this way the iron salt needed for the
coloring matter can be absorbed by the stone, and this be changed
afterwards to oxide by heating. The best carnelians come from India,
but good stones are also obtained in Siberia, Brazil, and Queensland.
Carnelians are cut usually in oval and shield-like shapes. They were
much employed by the ancients for intaglios, who believed them to have
the power of preventing misfortune, curing tumors, preventing
hoarseness, and strengthening the voice. They also insured victory in
all contests save those of love. Used as a powder or worn in a ring
carnelian was believed to prevent bleeding at the nose, and the belief
survives to some extent to the present day.
The name carnelian is, according to some authorities, derived from the Latin word caro, carnis, flesh, and refers to the color of the stone; according to others, it is from the Italian word carniola, which has the same meaning.
Sard, of
typical brown color, is much rarer than carnelian, and possesses a
higher value. The sardius mentioned in the Bible as forming one of the
stones of the high priest's breastplate, was undoubtedly a carnelian.
The name was derived from Sardius, a city of Lydia, whence fine
carnelians are obtained. Sard occurs with carnelian and grades into it.
The best sard should be of a deep brown color, shading to orange but
with a reddish tinge by transmitted light. The color can be
artificially produced by methods similar to those described below for
coloring agates, but long and careful treatment is required. The sard
was believed by the ancients to confer cheerfulness and courage and to
be a preventive of noxious humors.
Chrysoprase and prase are
terms applied to an apple-green to bright green chalcedony, or compact,
jasper-like form of quartz. Some authorities, however, call the green
chalcedony plasma, and restrict the term chrysoprase to the green
compact quartz. The terms cannot be accurately distinguished. Most
chrysoprase now in use comes from localities
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