PHYSIOGRAPHY. 243 



Tourmaline. 



ly striated, parallel to the axis ; k rough, the rest of the 

 faces generally smooth, and of nearly the same physical 

 quality. 



Lustre vitreous. Color, brown, green, blue, red, white, 

 frequently black ; generally dark colors, rarely bright. 

 Streak white. Transparent . . . almost opake, agreeably to 

 the color. Less transparent if viewed in a direction paral- 

 lel to the axis than when perpendicular to it, and generally 

 different colors in these directions. 



Hardness = 7-0 ... 7-5. Sp. gr. = 3-076 ; = 3-021, 

 transparent Rubellite from Paris; =3-009, of a transpar- 

 ent green variety from Paris; =3-055 of transparent In- 

 dicolite from Paris. 



Compound Varieties. Massive : composition seldom 

 granular, of various sizes of individuals ; generally colum- 

 nar, of various sizes of individuals, often very thin, straight 

 and parallel or divergent; sometimes again aggregated into 

 larger granular, or wedge-shaped masses ; faces of compo- 

 sition smooth and longitudinally streaked. 



1. Tourmaline and Schorl were formerly distinguished as two par- 

 ticular species, though they differ in no other respects than in color and 

 transparency. Tourmaline included the green, blue, red, brown and 

 white color, (the blue being called Indicolite and the red Rubellite) , 

 while Schorl comprised the black varieties. 



2. This species offers a variety of results when heated before the 

 blow-pipe. Some varieties (especially those containing lithia) intu- 

 mesce and assume a slaggy appearance, but do not melt; others (which 

 contain lime) intumesce still more and melt into a white slag. It as- 

 sumes by heat, opposite kinds of electricity on the opposite ends of the 

 crystals. The finest, transparent crystals, especially when cut by the 

 lapidary, are constantly electric without artificial heat. 



