PHYSIOGRAPHY. * 239 



Topaz. 



Cleavage ; parallel with P highly perfect ; with n im- 

 perfect ; traces of M and I. Fracture more or less per- 

 fectly small conchoidal, uneven. Surface, P rough, some- 

 times faintly striated, parallel to the edges of combination 

 with I. The vertical planes always striated, sometimes 

 deeply, parallel to their common edges of combination. 

 The pyramidal planes always smooth. 



Lustre vitreous. Color, white, yellow, green, blue, va- 

 rious, but generally pale shades. Streak white. Trans- 

 parent . . . translucent, sometimes only on the edges. 



Hardness = 8*0. Sp. gr. = 3*499, of a transparent 

 crystallized variety ; = 3'494 variety Pycnite. 



Compound Varieties. Massive : composition granular, 

 of various sizes of individuals ; faces of composition rough. 

 There occurs also columnar composition, the individuals 

 being thin, long and parallel, and easily separated, and their 

 faces of composition longitudinally streaked. 



1. Two varieties of Topaz have been treated of by many writers as 

 distinct species : viz. the Physalite and Pycnite. The first of these 

 consists of imbedded crystals, whose surface is rough and uneven, or 

 large massive individuals, whose color is a pale greenish grey. The lat- 

 ter occurs in thin and straight columnar particles of composition, forming 

 larger or smaller imbedded masses, and not possessing bright colors or 

 high degrees of transparency. 



2. In a strong heat, the faces of crystallization, but not those of cleav- 

 age, are covered with small blisters, which however, immediately 

 crack. With borax, it melts slowly into a transparent glass. Its pow- 

 der colors the tincture of violets green. Those crystals which possess 

 different faces of crystallization on opposite ends, acquire different kinds 

 of electricity on being heated. By friction, it acquires positive elec- 

 tricity. 



