ORES OF ALUMINIUM 153 
from bauxite, of which there are large supplies in the tropics 
and warm temperate zones. 
The production of aluminium has increased rapidly in 
recent years; the total output in 1913 was 70,000 tons, 
which the stimulus of the War raised to 178,000 tons in 1918, 
and after a fall to 67,000 tons in 1921, increased to 190,000 
tons in 1925. The modern production is mainly from the 
mixed mineral bauxite, which was described by Berthier 
in 1821 from Les Baux near Arles in the S. of France; it 
contains 52 per cent. of alumina. An allied material from 
Southern India had been named laterite by Buchanan in 
1807; it is an oxide of alumina associated with ferric oxide, 
titanium oxide, and water. Laterite is a superficial decom- 
position product of various rocks, and especially basalt, in 
warm countries with a long dry season. 
Bauxite—Bauxite has been often regarded as a mineral 
species with the composition Al,O,, 2H,O, and therefore 
intermediate between diaspore, AlO;, H,0, and gibbsite, 
ALO, 3H,0, and also allied to wocheinite, 2A1,0,, 3H,0. 
Some bauxite is a mixture of equal parts of gibbsite and 
diaspore, and some of that in India, according to C. S. Fox 
(Mem. G.S. India, xlix, 1923, p. 21) consists of gibbsite mixed 
with amorphous alumina and iron oxide. = Bauxite and 
laterite pass into one another, the laterite having more iron 
and bauxite more alumina. Both are formed by the de- 
composition of silicate of alumina and removal of silica. 
Silicate of alumina is usually stable, but is decomposed in 
nature by three processes. Where rain-water soaks into the 
ground and acts upon it slowly in the presence of carbon 
dioxide and organic matter or—as suggested by Sir Thomas 
Holland (Geol. Mag. 1003, p. 63) of primitive organisms 
such as bacteria—the silicate is decomposed ; the water 
carries silica into the rivers in solution (e.g. Sir J. B. Harrison, 
Rep. Geol. Brit. Guiana, 1898, p. 19), or deposits it as veins 
of quartz, leaving free alumina which is widespread in 
tropical soils. The alumina is often deposited in rounded 
concentric bodies or pisolites. This process is especially 
effective where hot dry seasons alternate with periods of 
heavy rain, where the slope is gentle, so that the rain soaks 
Into the ground, and at levels, as below 5000 feet in India, 
where the average temperature is high throughout the year.