Sapphire is a type of corundum. It occurs in every color except red, because red corundum is
ruby. It is actually more durable than diamond, even though diamond can't be scratched. Durability in this case refers to corundum'
s ability to withstand wear and tear.
Some sapphires grow in the earth in such a way that when they are
cut cabochon style (which is basically a smooth, domed shape), they display a
six-rayed star that moves around as the
stone is moved around a fixed light source. This is refered to as "asterism".
The Rockefeller Sapphire,
blue, 62 carats.
The Star of India, grayish
blue, 563 cts.
The Star of Asia,
blue, 330 carats.
The Stuart Sapphire, blue, 104 cts.