discovery
of the law of double refraction, and later, Malus to the discovery of
polarized light. It is employed in optical instruments for its strong
double refracting power, (see Calcite).
Ilmenite:
Iron Oxide. Composition varies. It occurs usually in large homogeneous
masses, in granular aggregates, in thin plates and sand grains, but
rarely in crystals. Because of its abundance, attempts have been made
to utilize Ilmenite as an ore of iron, but on account of the presence
of titanium it has not been satisfactory. With improvements in electric
smelting, it may soon become an important source of iron. It occurs in
many places in Europe and the United States.
Indicolite: A blue or bluish-black variety of Tourmaline.
lodyrite:
Silver Iodide. Iodine 54%, Silver 46%. A valuable but rare ore of
Silver occurring in thin plates, massive and in crystals. Color
citron-yellow, and sulphur-yellow
to yellowish-green. Is found in Mexico, Spain and Chile; also in
Arizona, New Mexico and Utah.
Iolite:
Sometimes called "Water Sapphire." It is a rare semiprecious stone,
and like Tourmaline, shows a different shade of color when viewed from
different directions, which gives
to cut stones an attractive change of color, from deep blue to yellow.
Iridium:
A metal of whitish color found in the ore of Platinum in the Urals and
Brazil. The name is from a Greek word meaning rainbow, so-called
because of the changing color of some of its salts. It occurs
generally in angular grains but rarely as crystals.
Iron: The
commonest and most useful of all metals. Cast-iron contains about 3.5%
carbon; wrought-iron about .4%. Between the two, is steel, containing
about 1 % carbon, and possessing properties that render it perhaps the
most important form in which iron is employed The range of its
application extends from the minute and delicate balance wheel of a
watch, to the large and ponderous battle-ship.
Magnetite
is a magnetic form of iron; meteoric iron is usually alloyed with
cobalt and nickel; pig-iron is iron cast in "pigs" or oblong masses.
Iron
occurs in small grains and large masses, but rarely in crystals. The
native metal a/ways contains some nickel. The most common occurrences
are in Meteorites. Over 100 localities have been
