PHYSIOGRAPHY. 



Tin-Ore. 



235 



Fig. 438. 



Small reniform, rarely botryoidal shapes : composition 

 very thin columnar, divergent from common centres, strong- 

 ly connected, and often forming a second curved lamellar 

 composition. Massive : composition granular, sometimes 

 almost impalpable, strongly connected, fracture uneven. 

 The hardness of very thin columnar compositions is often 

 found as low as 5-5, owing to the delicacy of the individu- 

 als in this composition. 



1. The Wood- Tin of the Cornish miners is only a variety of Tin- 

 Ore, in the same manner as Red Hematite is of Specular Iron. 



2. When heated in the pla(ina forceps before the blow-pipe, it is unal- 

 terable. Upon charcoal, in a strong heat, it is reduced to the metallic 

 state. The reduction is promoted by the addition of carbonate of soda. 

 It is not attacked by acids. Fused with caustic potash, it yields a mass, 

 which is mostly soluble in water. Muriatic acid, added to the solution, 

 occasions a while precipitate, which is again dissolved. Hydriodic acid 

 produces a yellow precipitate. 



3. Analysis. 

 By KLAPROTH. By DESCOTILS. 



Crystallized var. Compound var. 



Oxide of tin . . 99-00 . . . 95-00 

 Oxide of iron . . 0-25 . . . 5-00 



Silica . . 075 . . . 0-00 



4. Tin-Ore occurs disseminated in rocks, particularly in granite ; also 

 in beds and veins. It is frequently accompanied by Wolfram and Molyb- 



