234 



PHYSIOGRAPHY. 



Tin-Ore. 



s on s 



s on s over g 



z on z 



z on z over r 



r on r 



Cornwall. 



- 121 35' 



87 17 



- 159 6' and 118 16 



135 17 



- 112 27' and 157 23 



Frac- 



Cleavage, s and g not very distinct, traces of P. 

 ture imperfectly conchoidal, uneven. 



Surface, g often uneven, s sometimes irregularly striated 

 parallel to the edges of combination with P, and the latter 

 pyramid parallel to those with s. The prisms are some- 

 times vertically streaked. 



Lustre adamantine. Color various shades of white, 

 grey, yellow, red, brown, black. Streak pale grey ; in 

 some varieties, it is pale brown. Semi-transparent, some- 

 times almost transparent . . . nearly opake. 



Brittle. Hardness = 6*0 . . . 7-0. Sp. gr. = 6-960, a 

 crystallized variety ; =6*514, thin columnar composition; 

 = 7*100, from Cornwall. 



Compound Varieties. Twin-crystals : axis of revolu- 

 tion perpendicular, face of composition parallel to one of 

 the faces of P. 



