Corundum
Corundum
An aluminum oxide, it occurs as shapeless grains and masses (emery), rhombohedral crystals. Ruby contains traces of chromium oxide, when red and Fe2O3, which modified the color. The color of sapphire results from a combination of titanium and iron oxides, when a Fe+2 and a Ti+4 substitute the aluminum Al+3 or a Fe+3 and a Ti+3 substitutes the aluminum Al+3. Star sapphires and rubies show asterism of 6-rayed star. Cat’s-eye sapphire is very rare. It is the second hardest mineral after diamond. Sometimes call hard spar, diamond spar, adamantine spar and corindon. Some impure stones, show a silk effect, have minute, needle-like inclusions of rutile, and are cut as star rubies, star sapphires and cabochon, asterism or with cat’s eye (one ray) effects. Pure synthetic crystals are used in the laser industry. Sometimes the word oriental as a prefix, is used which is a misnomer other than the red variety that is called oriental ruby. Corundum is distinguished from other stones of similar appearance by their vitreous luster weak color dispresion, double refraction, high specific gravity, dichroism by colored stones or by microscopical examination. It is the birthstones for July. Pigeon blood ruby is a purplish deep red from Mogok in upper Myanmar, (Burma). padmaragaya is a Singhalese (Ceylonese or Sri Lankan) term for orange colored corundum, which means lotus flower. It was named as carbuncle with many other red stones such as spinel (ballas ruby) and garnet. Used as abrasive such as common corundum or emery, transparent crystals such as ruby, which are red in color and sapphire in blue, or other colors are fashioned as brilliant cut, step-cut, emerald-cut, mixed-cut.