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TOPAZ.
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The
price of spinelles it is difficult to determine with accuracy, as
much depends on their properties ; if perfect and exceeding four
carats, they are usually worth half the price of diamonds equally
large. The spinelle ruby and balais ruby are the most esteemed
spinelles, and if of twenty-four to thirty carats, are worth from two
hundred to four hundred francs ; and such gems are often sold for true
rubies (sapphire).
Zircon
is of greater specific gravity and less hardness than the spinelle, and
shows strong and double refraction of light. Calcined topaz is
distinguished by its electric properties. Burnt amethysts are lighter,
and are scratched by spinelle. Pastes are likewise substituted for the
spinelle, such as glass colored with gold-purple ; but as the spinelles
are always harder and heavier, the adulterations may soon be detected.
According
to Mr. Ebelman, the artificial spinelle is obtained by the following
mixture, which is put into a platina capsule and exposed to the heat of
a porcelain furnace :
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TOPAZ.
It
is not determined whether the ancients meant by topaz the same geni as
we describe, since the Greeks understood the topaz to ba of a
transparent gold-yellow, and the Romans, of a transparent green-yellow.
The name, which, according to Pliny, is derived from Topazos, an island
in the Red Sea, has no reference to its color. Topaz was, in former
times, thought to possess great medicinal virtyes ; for example, as a
remedy for mania, and as a
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