Sapphire is the name for all gemstones in the Corundum mineral group, apart from the Red variety which is called Ruby. When used alone the name Sapphire assumes Blue Sapphire. Corundum is the second hardest mineral on earth, just below the hardest mineral, Diamond.
Sapphire gets it’s colour from trace amounts of elements such as iron, titanium, chromium, copper, vanadium or magnesium. These impurities can give corundum blue, yellow, pink, purple, orange, or greenish color.
Sapphire is the birthstone for September. The largest Sapphire in existence is the 423-carat (85 g) Logan sapphire which is housed in the National Museum of Natural History, in Washington, D.C.
In the middle ages it was said that Sapphire preserved chastity, discovered fraud and treachery and protected from poison, plague, fever and skin diseases.
In the gem industry, color in gemstones is referred to in three components: hue, saturation, and tone. Hue is the “[color]” of the gemstone. Saturation refers to the strength/depth of the color of the gemstone or ‘colorfulness’ and tone is the light to dark of the color. Songea Sapphires deserve a special mention here: these are bright Sapphires in shades of orange, red, tangerine, saffron, golden yellow and green. They are mined in Tanzania and treated in Thailand to change the color. More is mentioned in the section on treatment. Padparadscha is a pink-orange sapphire; the rarest of all has no signs of treatment. Star Sapphire are common; the clearer the star and stronger the base color, the higher the value. Diffusion treated star stones are common in the marketplace.
Hardness on Mohs Scale: 9
Specific Gravity: 3.58 – 3.61
Refractive Index: 1.712-1.740 Cleavage: None
General Chemical Formula: A2+B23+O42-
Crysta lform: Sapphire crystals occur as barrel shaped, double pointed hexagonal pyramids and tabloid shapes. Corundum is generally found in metamorphic rocks and in alluvial gem gravel deposits. Sapphire may also be found in pegmatites.
Rutile inclusions or ‘silk’ maybe in clusters, guest crystals (calcite) maybe in lines, liquid finger print inclusions, two phase inclusions.
Indication of heat treatment are: a tension ‘halo’ around a crystal inclusion, melted solid inclusions, discoidal fractures, signs of diffusion of silk.
Indication of beryllium treatment are: feather, tubular or cotton wool type inclusions.
Specific inclusions by Sapphire origin:
Sri Lanka/Ceylon: crystal inclusions of Mica, pyrite, zircon crystals with halos, elongated negative crystals, two phase inclusions.
India/Pakistani Kashmir: milkiness from tiny inclusions.
Burma: long rutile needles, apatite crystals, convoluted feathers, silk, maybe hexagonal color zoning.
Ratnapura: Sri Lanka, Mogok: Burma, the UmbaValley: Tanzania – also Songea and Tunduru. Indian/Pakistani, Kashmir, Australia, Thailand, Vietnam
Just like Diamonds, Sapphires are graded according to the Four C’s of Cut, Clarity, Color and Carat. Purity and intensity of color is paramount. Few black undertones and a violet overtone of up to 15% is what the valuers recognize as the best blue Sapphire.
Padparadscha sapphires can attract higher prices than the finest blue sapphires if unheated. Sapphires with more than one color are becoming very collectible and starting to attract higher prices; they are a good investment. Treatment of Sapphires also greatly affects the value. An unheated Sapphire will sell for far more than a heated one. But with Sapphires this is only the beginning of what you need to know; see the next section.
Now That You Know About Sapphires, Go Shopping!
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