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MINERAL RESOURCES.
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little phosphorus. Melted iridium is a brilliant white, brittle metal. Its hardness is 6.7, surpassing that of platinum.
Osmium.—Osmium
occurs generally as an alloy with iridium, in which the other metals of
the group are very subordinate. The mineral called iridosmine forms
hexagonal crystals or flattened grains and has a white color
considerably lighter than that of platinum. It contains from 40 to 77
per cent iridium and from 20 to 50 per cent osmium.
The metal in refined state is bluish gray, hard, and brittle and oxidizes rather easily.
Palladium.—Palladium
is a white metal, intermediate in color between platinum and silver.
Its hardness is about equal to that of platinum. It is malleable,
ductile, and sectile, and dissolves easily in nitric acid. Palladium is
present in almost all varieties of crude
p
latinum, but the
analyses rarely show more than 2 per cent. In larger quantities it is
present in some copper ores, but its state of combination is in doubt.
Probably it is combined with arsenic, like sperrylite.
Rhodium.—Rhodium
is a white metal of the color of aluminum. It is ductile and malleable
at red heat. The metal occurs in crude platinum in quantities up to 4
per cent. Like palladium, it probably occurs in combination with
arsenic in certain copper ores.
Ruthenium.—Ruthenium
is a white, hard, and brittle metal, which is scarcely attacked by aqua
regia. Like osmium, it oxidizes rather easily in the air. It is found
to small extent in crude platinum, but mainly occurs to the extent of a
small percentage in the mineral iridosmine.
Other platinum minerals.—Very
few platinum minerals are known beyond those already mentioned.
Sperrylite or arsenide of platinum (PtAsj), with a little antimony and
rhodium, occurs as small crystals of an isometric form and tin-white
color in certain copper and nickel ores—for instance, at Sudbury,
Ontario, and at the New Rambler mine, Wyoming. The minute crystals are
embedded in pyrrhotite or covellite.
Laurite
is an extremely rare sulphide of ruthenium with a minor amount of
osmium. It is known only from the platinum washings of Borneo.
Palladium
in quantities up to 10 per cent also occurs in combination with gold.
This mineral, called porpezite, has been described from Brazil, where
it occurs in gold-bearing veins.
Platinum
has been found in some varieties of tetrahedrite and bournonite. In
minute quantities it occurs in some quartz veins, mainly of the
so-called "high-temperature class," for instance, in northern Finland
and in the gold-bearing veins of Beresowsk, Russia. Occasionally
platinum is found in clay shales and in coal ashes, but so far not in
recoverable quantities. Platinum is present in some meteorites and in
the sun.
DETERMINATION OF THE PLATINUM METALS.
The
correct determination of platinum metals is somewhat difficult, and
mistakes are often made by inexperienced chemists and assay-ers. It is
difficult, to say how much of the mistakes found in reports of new
discoveries of platinum in the current press is due to such
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