ORDER Yin. PYRAMIDAL TIN-ORE. 



6. P. P + 1. (P) 5 . [P + oo]. (P + oo) 5 . 

 Fig. 103. Cornwall. 



Cleavage, P 4- oo and [P -f- oo] not very distinct, 

 traces of P. Fracture imperfect conchoidal, 

 uneven. Surface, P QD rough, [P -f- oo] of- 

 ten uneven ; P -f 1 sometimes irregularly striat- 

 ed parallel to the edges of combination with P, 

 and the latter pyramid parallel to those with 

 P -+ 1. The prisms are sometimes vertically 

 streaked. 



Lustre adamantine. Colour various shades of white, 

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

 grey, in some varieties it is pale brown. Semi- 

 transparent, sometimes almost transparent ... 

 nearly opake. 



Brittle. Hardness = 6-0 . . . 7-0. Sp. Gr. = 6-960, 

 a crystallised variety; =6-519, thin columnar 

 composition. 



Compound Varieties. Twin-crystals: Axis of 

 revolution perpendicular, face of composition par- 

 allel to one, or sometimes to several faces of P. 

 Small reniform, rarely botryoidal shapes : original 

 surface rough, composition very thin columnar, di- 

 vergent from common centres, strongly connected, 

 and often forming a second curved lamellar com- 

 position. Massive : composition granular, sometimes 

 almost impalpable, strongly connected, fracture un- 

 even. The hardness of very thin columnar com- 

 positions is often found as low as 5'5, owing prob- 



VOL. II. 2 B 



