the red variety of corundum
VARIETY OF: Corundum
, Al2O3 .
BIRTHSTONE FOR: July
COLOR: various shades of red.
INDEX OF REFRACTION: 1.76 - 1.78
CLEAVAGE: none, although there is a rhombic parting
CRYSTAL SYSTEM: trigonal
For natural ruby mineral specimens see our For Sale or Sold lists
Ruby is the red variety of corundum, the second hardest natural mineral
known to antiquity. The non-red variety of corundum is Sapphire.
Sapphires are well known among the general public as being blue, but can
be nearly any color. The red color in ruby is caused by trace amounts of
the element chromium. The best shade of red for ruby is often given the
name "pigeon blood red", but ruby can be any shade of red up
to almost pink.
crystal inclusions cause a six-rayed-star light effect (called asterism)
to form the popular Star Ruby.
Rubies come from all over the world but
good gemstones are found at Thailand, India, Madagascar, Zimbabwe, North
Carolina in the U.S., Afghanistan, Pakistan, Sri Lanka, Kenya, Tanzania,
Kampuchea, and perhaps most notably, Burma.
Rubies have a famous place in science - the first lasers were made from
artificial ruby crystals. They still are used for this purpose although
other materials offer improved efficiency. Some ruby crystals show the
fluorescence (actually very short term phosphorescence) that makes a laser