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Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite)

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CHAPTER IV.
Topaz and Tourmaline (Rubellite, Indicolite, and Achroite).
T OPAZ crystallizes in the orthorhombic system, and oc­curs in prisms with one end regularly terminated, and has a very perfect cleavage transverse to the prism. Its hardness is 8, and specific gravity 3'53. It is a silicate of alumina containing fluorine. A blue crystal weighing 20 pounds is in the Imperial Mining School at St. Petersburg, Russia. Fine blue and sherry colored crystals have been found in Siberia, blue ones in Scotland and Ireland, yellow in Minas Geraes, Brazil ; white in Villa Rica, Brazil ; and blue and white in Ceylon and Australia. Brazilian or true mineralogical topaz is often confounded with two other minerals, namely, citrine and Spanish or Saxon topaz, the color of which is made by heating and so decolorizing smoky quartz to various shades of yellow or brown. Yellow sapphire is called Oriental topaz. The specific gravities of the three varieties are given for comparison.
True yellow topaz, if heated for a time, becomes pink, and continued heating renders it colorless.
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Ch. 3: Turquoise Page of 364 Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite)
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