mption that alumina has remained constant, eastern
Cuba.]

The Cuban iron ores are similar in their origin to _laterites_, which
are surface accumulations of clay, bauxite, and iron oxide minerals,
resulting from the weathering of iron-bearing, commonly igneous, rocks.
The typical laterites carry more clay and bauxite than the Cuban iron
ores, but this is due merely to the fact that the original rocks
commonly carry more materials which weather to clay. In fact the Cuban
iron ores are themselves, broadly speaking, laterites.

=Iron ores due to weathering of sulphide ores.= A relatively minute
portion of the world's iron ore comes from the "gossans" or "iron caps"
over deposits of iron sulphides. The gossans are formed by oxidation and
leaching of other minerals from the deposits, leaving limonite or
hematite in concentrated masses (see pp. 46-47).

MANGANESE ORES

ECONOMIC FEATURES

Manganese ores are used mainly in the manufacture of steel, the alloys
spiegeleisen and ferromanganese being added to the molten steel after
treatment in the Bessemer converter and open-hearth furnace in order to
recarburize and purify the metal. The alloy ferromanganese is also used
in the production of special manganese steels. Manganese ore is used in
relatively small amounts in dry batteries, in the manufacture of
manganese chemicals, in glass making, and in pigments. Steel uses 95 per
cent of the total manganese consumed, batteries and chemicals 5 per
cent. On an average each ton of steel in the United States requires 14
pounds of metallic manganese, equivalent to 40 pounds of manganese ore.

With manganese ores, as with iron ores, the percentage of minor
constituents,--phosphorus, silica, sulphur, etc.,--determines to a large
extent the manner of use. Low-grade manganese ores, ranging from 10 to
35 per cent in manganese, 20 to 35 per cent in iron, and containing less
than 20 per cent of silica, are used mainly in the production of the
low-grade iron-manganese alloy called _spiegeleisen_ or _spiegel_ (16 to
32 per cent manganese). The higher-grade ores, ranging from 35 to 55 per
cent in manganese, are used mainly in the production of the high-grade
alloy called _ferromanganese_ or _ferro_, in which the manganese
constitutes 65 to 80 per cent of the total. To a very limited extent
manganese is smelted directly with iron ores, thus lessening the amount
to be introduced in the form of alloys; this, however, is regarded as
wastef