It is infusible
before the blowpipe. It becomes electrical by rubbing, and retains its
electricity for several hours; but does not become electrical by
heating. It occurs in alluvial soil, in the vicinity of rocks belonging
to the secondary or floetz-trap formation, and imbedded in gneiss. It is
found at Rodsedlitz and Treblitz in Bohemia, and Hohenstein in Saxony;
Expailly in France; and particularly beautiful in the Capelau mountains,
twelve days from Sirian, a city of Pegu. Next to diamond it is the most
valuable of gems. The white and pale blue varieties, by exposure to heat
become snow-white; and when cut, exhibit so high a degree of lustre,
that they are used in place of diamond. The most highly prized varieties
are the crimson and carmine red; these are the oriental ruby of the
jeweller; the next is sapphire; and the last is sapphire, or oriental
topaz. The asterias, or star-stone, is a very beautiful variety, in
which the colour is generally of a reddish violet, with an opalescent
lustre. A sapphire of ten carats weight is considered to be worth fifty
guineas.--_Jameson_.
The blue topaz, or Brazilian sapphire, is of recent introduction.
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