The name "Ruby" (Rubis French, Rubin German, Rubino Spanish or Italian) is Latin for red. The fiery red color of ruby was thought to be an inextinguishable flame lit from within. Rubies were celebrated in the Bible and in ancient Sanskrit writings as the most precious of all gemstones. Ruby is also known as the "stone of Kings". Some of the finest rubies in the world are mined in Myanmar and Thailand. Other significant sources for rubies include Kenya, Afghanistan (Jagdalek, Jagdalak, or Jagdalik), Madagascar, Pakistan, Sri Lanka, Tanzania, and Vietnam.
The ruby belongs to the same "aluminium oxide" mineral family (corundum) as sapphire and is formed by heat and pressure in limestone rich in clay. The primary origin of ruby is metamorphic rocks and volcanic igneous rock or basalt, and secondarily alluvial. Ruby is made up of the mineral corundum, which is aluminum oxide or alumina. It becomes a ruby when it has a small impurity of chromic (III) oxide (chromium) which gives it the rich red coloration. If the corundum has other impurities such as iron and titanium which will give it a blue color, it is called sapphire. Rubies can be transparent to totally opaque, and have a vitreous to dull greasy luster.
Ruby and sapphire gems also sometimes exhibit a six-pointed "star" or "asteriated" effect from reflection off microscopic, needle-shaped rutile crystals (also referred to in the ruby trade as "silk") which intersect at 60° angles. Star rubies are semi-transparent to opaque, and the star effect is more apparent when a cabochon cut is used for the stone.
Ruby has a hardness of 9 on the Mohs scale. Corundum has no cleavage planes, but does have a conchoidal fracture, and can be parted more easily in certain directions. The Toughness of Ruby is Excellent. Ruby is categorized in the hexagonal crystal system with a tabular crystal habit. Ruby has a refractive index of 1.760. Rubies are commonly subjected to artificial enhancements such as heat-treating, fracture-filling, flux-healing to improve color and repair fractures and inclusions.
Chemical composition: BeAl2O3
Rutile (Silk) Inclusions in Ruby
Mogok's rubies are typically euhedral (well-formed) rounded crystals with rutile or "silk" inclusions occurring as patches, zoning or overall cloudiness. Rhombohedral twinning is common, along with straight/angular color-zoning. Mogok rubies are usually free of the water-filled inclusions that are common in Cambodian, Thai, or Sri Lankan rubies. Mogok stones have distinct pyramid and/or bi-pyramid domes, terminated by the basal pinacoid.
Color Zoning & Pleochroism in Ruby
Color zoning is a phenomenon caused by growth layers as the corundum crystal is formed. These layers create distinct areas of color that appear as concentric hexagonal zones that are parallel to the prismatic crystal faces. Möng Hsu rubies tend to have a distinct dark blue hexagonal zone at the center of the stone.
Ruby can display strong pleochroism when viewing the specimen from different angles, appearing as either a deep red or a yellowish-red.
On To:
Burmese Mogok Ruby
Rubies from Sri Lanka (Ceylon)
Map of the Mogok Stone Tract
Map of the Mong Hsu Stone Tract
Ruby Enhancements - Fracture Filling & Flux Healing
