Sapphire (Greek: ?????????; sappheiros, "blue
stone"[1]) is a gemstone variety of the mineral
corundum, an aluminium oxide (?-Al2O3), when it
is a color other than red or dark pink; in which
case the gem would instead be called a ruby, considered
to be a different gemstone. Trace amounts of other
elements such as iron, titanium, or chromium can
give corundum blue, yellow, pink, purple, orange,
or greenish color. Pink-orange sapphires are also
called padparadscha. Pure chromium is the distinct
impurity of rubies. However, a combination of
e.g. chromium and titanium can give a sapphire
a color distinct from red.
Sapphires are commonly worn as jewelry. Sapphires
can be found naturally, by searching through certain
sediments (due to their resistance to being eroded
compared to softer stones), or rock formations,
or they can be manufactured for industrial or
decorative purposes in large crystal boules. Because
of the remarkable hardness of sapphires (and of
aluminum oxide in general), sapphires are used
in some non-ornamental applications, including
infrared optical components, such as in scientific
instruments; high-durability windows (also used
in scientific instruments); wristwatch crystals
and movement bearings; and very thin electronic
wafers, which are used as the insulating substrates
of very special-purpose solid-state electronics
(most of which are integrated circuits).
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