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Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide
(Al2O3), a mineral known as corundum. It can be found naturally as gemstones or
manufactured in large crystal boules for a variety of applications.
Since sapphire ranks a 9 on the Mohs Scale, owners of such watches should still be
careful to avoid exposure to diamond jewelry, and should avoid striking their
watches against artificial stone and simulated stone surfaces. Such surfaces often
contain materials including silicon carbide, which, like diamond, are harder than
sapphire and thus capable of causing scratches (Scheel 2003).
Wafers of single crystal sapphire are also used in the semiconductor industry as a
substrate for the growth of gallium nitride based blue and green light-emitting
diodes.
According to Rebbenu Bachya, the word "Sapir" in the verse Exodus 28:20 means
"Sapphire" and was the stone on the Ephod representing the tribe of Issachar.
However, this is disputed as the sapphire of the bible was likely lapis lazuli (Texas
Natural Science Center, 2006). Sapphire is the birthstone associated with
September. Lady Diana Spencer's engagement ring from Charles, Prince of Wales
was a sapphire ring.
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