232 A POPULAR TBEATISE ON GEMS.
stones ; this is effected by calcining them first, then throwing them into water, and afterwards pulverizing them.
By
heat the topaz assumes a pink or red hue, so nearly resembling the
balais ruby that it can only be distinguished by the facility with
which it becomes electric by friction.
Topazes
from New South Wales, Brazil, and Scotland, sometimes contain cavities,
in which Sir David Brewster discovered two fluids, one of which has an
index of refrac-tion=l-211, and expands 0'25 of its original volume on being heated, from 10° to 27°.
The
topaz is found green, blue, and colorless at Ala-baschkka Meersinsck,
Miask, and Aduni Tschelon in Siberia ; Kamtschatka, Peru, and Rozena
in Moravia, with lep-idolite ; Mucla in Asia Minor, Peneg in Saxony,
and at Schneckenstein, near Auerbach, in Saxony, of a wine-yellow
color; at Villa Rica, in Brazil, of a deep-yellow color; with tin ore
at Geyer, Ehrenfriedersdorf, and Altenberg in Saxony, Schlackenwald in
Bohemia; with tin ore and apatite in veins of granite at St. Michael's
Mount and Huel-kind, near St. Agnes in Cornwall ; in granite in the
Morne mountains in Ireland ; in the United States, at Trumbull and
Middletown, Connecticut.
The
less transparent variety (pyrophysalite), with fluor in granite veins,
at Tinbo, near Fahlun, in Sweden ; in boulders at Braddbo, in Sweden ;
in gneiss at Fossun, in Norway.
Topaz
is generally of less value now than formerly, owing to the yearly
supplies obtained from Brazil, which is about forty pounds. The mine at
Capao has yielded about twelve thousand dollars' worth, and the supply
has been accumulating at Rio de Janeiro and Bahia to such a degree,
that it is disposed of at a less price there than at the mines.
Those most esteemed are the rose-red and the white, or water drops, pingos d' agoa. A topaz ofthe size of a bean is sold at Chapada, in the Termo Minas Novas, at one
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