78 
ECONOMIC GEOLOGY 
from a wide outcrop would have been scattered and only the 
poorer marginal deposits left. 
VARIATIONS IN PricE oF Tin—For many years the normal 
price of tin ranged a little below £100 a ton; in 1916 it was 
£162 a ton, in 1920, £423 a ton, and after falling to £130 
in 1922, rose in 1926 to over £300 a ton. The price has been 
subject to sudden fluctuations, and ore deposits that were 
FiG. 27.—RELATION OF THE Wipte OF GRANITE 10 Tin PLACERS. 
Relation of the width of granite outcrop to richness of tin placers. The 
surface at A would bear washings from the tip of the granite which 
is rich in cassiterite. In the surface at B, the poor lower margin of 
the granite is exposed and the alluvial tin ore will be less abundant. 
The cassiterite in the granite represented by black dots, 
paying well are for a time rendered worthless. Sensational 
statements made during a quarrel between two groups of 
Chicago meat packers led to a fall in the demand for canned 
meat, and therefore for tinned plate, that closed nearly 
all the tin mines in Tasmania. The tradespeople at the 
mines were ruined, owing to a commercial quarrel at their 
antipodes. 
TUNGSTEN 
(W; sp. gr, 19:1; at. wt, 184 ; melting-point, 3100° F.) 
The main use of tungsten is for high-speed tool steel, which 
remains hard and tough to an almost red heat. As the 
melting-point of tungsten is high and its rate of expansion 
nearly the same as that of glass and platinum, it is used for 
electric lamps. It is also useful in dyes, and in colouring 
glass and porcelain. 
Source oF TuNGsTEN—Most of the supply is obtained 
from wolframite ((FeMn)WO,), which is an iron-manganese 
tungstate due to the intergrowth of ferberite, iron tung- 
state, and hubnerite, manganese tungstate. A small supply