240 PHYSIOGRAPHY. 



Topaz. 



3. Analysis. 



By BERZELITJS. 



Crystals. Physalite. Pycnite. 



Alumina - 57-45 - 57-74 - 51-00 



Silica - 34-24 - 34-36 - 38-43 



fluoric acid - 7-75 - 7"77 - 8-84 



4. Topaz enters into the composition of granitic rocks ; thus it forms 

 with Quartz and Tourmaline the Topaz-rock of Saxony. It occurs also 

 in irregular beds, either with Quartz and Mica, like the variety Pyc- 

 nite ; or with Feldspar, Quartz, Beryl, &c. like the Physalite. It is also 

 found in veins, traversing'gneiss, where it is associated with Fluor, Mica 

 and Wolfram, as at Trumbull, (Conn.) It is met with besides in tin 

 stream-works, and in the alluvial deposits of rivers along with other 

 gems. 



5. The most perfect crystals are found with Beryl in the Uralian and 

 Altai mountains, . and in Kamtschatka ; in Brazil, where they are met 

 with in loose crystals, and at Mucla in Asia Minor. They occur in the 

 Topaz-rock at Danneberb in Saxony, and at Ehrenfriedersdorf and Zinn- 

 wald associated with Tin-ore; in similar repositories at Schlaggenwald 

 in Bohemia and St. Michaels mount in Cornwall ; with Lepedolite near 

 Rozena in Moravia. Physalite is found at Finboand Broddbo near Fah- 

 lun in Sweden. Pycnite at Altenberg in Saxony. Topaz pebbles are 

 found in the stream-works of Eubenstock in Saxony, in the granitic dis- 

 tricts of Cairngorm in Aberdeenshire, and in New South Wales. 



But a single locality is known in the United States, which exists at 

 Trumbull, (Conn.) in a vein upwards of one foot in width, where it is 

 associated with Fluor, Magnetic Pyrites, Mica, and rarely with Wolfram 

 and Tungsten. The Topaz is chiefly white, but when imbedded in the 

 magnetic Pyrites its color is green. It presents small druses occuring in the 

 veins, lined with tolerably perfect crystals, which are white and trans- 

 parent. Occasionally the crystals are several inches in diameter, and 

 perfect in some of their planes, but they are generally deficient in 

 transparency and lustre. Rarely, the massive individuals and imperfect 

 crystals are six or eight inches in diameter. 



6. It is much used as an ornamental stone. The blue varieties are 

 called Oriental Aquamarine, by Lapidaries. If exposed to heat, the 

 Topaz from Saxony loses its color and becomes white ; the deep yellow 

 Brazilian varieties assume a pale pink color, and are then sometimes mis- 

 taken for Spinel, or Ballas-ruby. 



