Diamonds and precious stones, a popular account of gems .. . analysis of specimens broughtfrom different localities proves that occidentaltopazes are not identical. They have for a longtime been divided into four varieties:— Brazilian Topaz. I Mexican Topaz. Saxon Topaz. I Siberian Topaz. It should be remarked, however, that while theproportions of the elements differ in each of thesevarieties, their nature is the same. The occidentaltopaz is in all cases formed of alumina, silica, andfluoric acid. The presence of this last substance,found in no other precious stone, characterizes per-fectly t
Diamonds and precious stones, a popular account of gems .. . analysis of specimens broughtfrom different localities proves that occidentaltopazes are not identical. They have for a longtime been divided into four varieties:— Brazilian Topaz. I Mexican Topaz. Saxon Topaz. I Siberian Topaz. It should be remarked, however, that while theproportions of the elements differ in each of thesevarieties, their nature is the same. The occidentaltopaz is in all cases formed of alumina, silica, andfluoric acid. The presence of this last substance,found in no other precious stone, characterizes per-fectly the genus topaz in respect to chemicalcomposition. The primitive type of crystals of topaz is theright rhomboidal prism (Fig. 58). Certain modifications occur in the form of thesecrystals, which, joined to their colour, enable aperson to decide as to which of the varieties anytopaz in question belongs. THE TOPAZ. 129 The Saxon topaz generally occurs in the form ofa rhomboidal prism with a base; and its colourvaries from an orange yellow to a straw Fig. 58.—Type of Crystal of Topaz. The Brazilian topaz exhibits most frequently arhomboidal prism surmounted by a four-faced pyra-
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectgems, booksubjectprec
