CHAPTER V 
ORES OF TIN AND TUNGSTEN 
Tin Ores? 
Tin—Historic InTEREST—Tin (Sn from Latin stannum— 
the English name comes from the Greek, zinn ; at. wt., 118; 
5p. gr., 7-1 to 7-3; melting-point, 450° F.) the white metal, 
is of special historic interest from its influence on early 
culture and prehistoric trade; most of the Mediterranean 
supply was obtained by the Pheenicians from Cornwall. 
The present main use of tin is in * tinned plate,” as a thin 
alm preserves iron from rust and corrosion. 
; PxEuMaTOLYTIC ORIGIN—Tin is obtained from cassiterite 
(Sn0Q,), which occurs in altered granites. It has been pre- 
pared artificially by passing stannic fluoride (SnF,) with 
boric acid over hot lime; it was probably mainly formed 
by the decomposition of stannic fluoride (SnF,) by boric 
acid, producing tin oxide and some borate such as tour- 
maline, Many occurrences, however, such as stalactites, 
\mpregnations in buried timber, and pseudomorphs after 
felspar, are due to deposition from solution, as tin oxide is 
slightly soluble in boiling water.2 Tin pyrites or stannite, a 
mixed sulphide of copper, tin, and iron, has been mined in 
Cornwall, New South Wales, and Chile. 
Cassiterite being heavy and resistant of weathering re- 
mains as a residual mineral in alluvial deposits. It generally 
Pays to mine only where concentrated by denudation of tin- 
bearing granites. Tin ores of commercial value are remark- 
ably restricted in distribution (Fig. 25). The chief fields are 
! For the tin fields of the world and a full bibliography, see W. R. 
I ones, Tinfields of the World, 1925. 
Ct. Collins, Miner. Mag, iv, 1880, pp. 1, 103 ; Vv, 1883, p. 121.