SCHORL FAMILY.
61. The TOPAZ is a gem usually of a wine-yellow colour, but sometimes orange, pink, blue, and even colourless, like rock crystal; of a lamellar or foliated structure, harder than quartz, but not so hard as ruby.
It varies considerably in its crystallization; is 3½ times heavier than water; and, when placed upon any object, shows a double image of it.
The name of topaz is derived from an island in the Red Sea, where the ancients found a stone, but very different from ours, which they denominated topaz. The best topazes are of a deep colour, and are imported from Brazil; the most brilliant ones are supposed to be those of Saxony; but the latter are generally of very pale colour. This species of gem is found in many parts of Europe, but defective in transparency, and sometimes even opaque. It occurs in large crystals, and rolled masses, in an alluvial soil ([269]), in the upper parts of Aberdeenshire, Scotland; and in veins, along with tin-stone, at St. Anne’s, in Cornwall. Topazes, more than a pound in weight, have been found in Scotland.
Mr. Mawe speaks of a topaz mine at Capon, near Villa Rica, in Brazil. In two breaks or slips of the rocks, he says, there were little soft places where the negroes found the topazes by scraping in them with pieces of iron. He himself observed at least a cart-load of inferior topazes, any number of which he might have taken away; but all that he saw were defective and full of flaws.
These stones vary much in size; some, particularly those of Siberia, being extremely small, and others being upwards of an inch in thickness. In the Collection of Natural History at Paris there is a Brazilian topaz which weighs four ounces and a quarter. These stones are not sufficiently scarce to be, in general, much valued by the jeweller or lapidary. The deep yellow variety is preferred to the pale sort, although the latter is often superior to it both in size and hardness.
Figures have sometimes been engraved on the topaz; and these, when well executed, are of great value. In the National Museum at Paris there is a superb Indian Bacchus engraven on a topaz. The cabinet of the Emperor of Russia contains several fine topazes of this description.
Some of the coarse kinds of topaz are broken down, pounded, and used instead of emery for the cutting of hard minerals; and powdered topaz was formerly kept in apothecaries’ shops, and sold as an antidote against madness.
It is a somewhat singular circumstance, that, if the Saxon topaz be gradually exposed to a strong heat in a crucible, it will become white and, on the contrary, that Brazilian topazes by the same process become red or pink. By exposure to a still stronger heat, the Brazilian topaz changes its colour to a violet-blue.
Jewellers usually divide topazes into the following kinds: