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The Best and Most Comprehensive Guide to Sapphires in Los Angeles and on the Web!
Copyright © 2006 INTA GEMS, Inc. All rights reserved.
Star Sapphires
Star sapphires are unique "phenomenon" stones cut in a smooth dome or "cabochon" shape. When a distant point light source, such as the sun, shines over the stone a six legged star will appear to "float" over the smooth surface. The formation of this star phenomenon has baffled humans for centuries and added to the myth of their special powers. Nowadays, we know that this effect is actually created by the presence of rutile needles (known as "silk" in gemology) within the crystal. Only gems with a right amount of silk with the correct placement can produce the star effect.
Because of the fact that transparent and faceted sapphires are in such high demand around the world, most silk-containing rough stones are sent to be heated in order to minimize their internal structures. It is through this heating process that most rutile needles are lost through melting. This also leads in the increasing scarcity of fine quality star specimens in the market today. Fine quality star sapphires almost all come exclusively from Sri Lanka (Ceylon) and at INTA Gems & Diamonds, we only stock genuine Ceylon stars.
Unlike other sapphires, a star is one of the only corundum species whose natural and untreated state can easily be identified by the unaided eye. Because the rutile needles responsible for the star effect are readily destroyed by heating processes, those with a clear and distinct star can almost be visually confirmed to be unheated.
The cutting of star sapphires depends largely on the concentration of silk and color within the crystal. Oftentimes they are found to have large pavilions (bottom depths) or large crowns (tops), which had been necessitated to accentuate and/or maximize the star effect.
Cabochons
The cabochon is one of the most ancient styles of gem cutting and polishing. It was employed to showcase the pure essence of a gemstone's color through a rounded and smooth translucency. Some of the oldest and most spectacular jewelry pieces found in the world are made from cabochon sapphires.
The most common cabochons are blue sapphire cabochons. It is common for people to confuse cabochons with start sapphires. But the two are very different species. Though they both have a rounded and smooth surface (at least for the top), the cabochon sapphire does not have the star effect and will have in most cases a higher internal clarity. And because a cabochon is a non-faceted polish meant to bring out the raw color of the stone, it does not have that "glitter" or sparkle so much associated with faceted stones. It might be said that cabochons are for connoisseurs and purists of colors.