160 



DESCRIPTIONS OF MINERALS. 



Cassiterite. — Tin Ore. Tin Oxide. 



Dimetric. 

 1. 



In square prisms and octahedrons; often com- 



2. 



pounded. 1 A 1 = 121° 40' , 

 Al i (over the summit) 1112° 

 10', (over a terminal edge) 

 133° 31'. Cleavage indistinct. 

 Also massive, and in grains. 

 Color brown or black, with 

 . a high adamantine lustre when 

 X~~^\>7 in crystals. Streak pale gray 



^^Js to brownish. Nearly trans- 

 parent to opaque. H. =6-7. G. =6-4-7*1. 



Composition. Sn O e = Oxygen 21-33, tin 78-67 ; often con- 

 tains a little iron, and sometimes tantalum. 



B.B. alone infusible. On charcoal with soda, affords a 

 globule of tin. 



Stream tin is the gravel-like ore found in debris in low 

 grounds. Wood tin occurs in botryoidal and reniform shapes 

 with a concentric and radiated structure ; and toad's-eye tin 

 is the same on a small scale. 



Biff. Tin ore has some resemblance to a dark garnet, to 

 black zinc blende, and to some varieties of tourmaline. It is 

 distinguished by its infusibility, and its yielding tin before 

 the blowpipe on charcoal with soda. It differs from blende 

 also in its superior hardness. 



Obs. Tin ore occurs in veins in the crystalline rocks, 

 granite, gneiss, and mica slate, associated often with wolfram, 

 copper and iron pyrites, topaz, tourmaline, mica or talc, and 

 albite. Cornwall is one of its most productive localities. 

 It is also worked in Saxony, at Altenberg, Greyer, Ehren- 

 friedersdorf and Zinnwald; in Austria, at Schlackenwaldand 

 other places ; in Malacca, Pegu, China, and especially the 

 Island of Banca in the East Indies ; in Queensland and 

 Northern New South Wales, Australia, in large quantities ; 

 in Greenland. It occurs also in Galicia, Spain ; at Dale- 

 carlia in Sweden ; in Russia ; in Mexico at Durango ; 

 and Bolivia. In the United States it has been found spar- 

 ingly at Chesterfield and Goshen, Mass. ; in some of the Vir- 

 ginia goldmines ; in Lvme and Jackson, N. H. ; and in the 

 Temescal Range, California. 



General Remarks. — The principal tin mines now worked, are those 

 of Cornwall, Banca, Malacca, and Australia. 



The Cornwall mines were worked long before the Christian era. 



