General Information
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What are Star Sapphires? |
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What causes the “Star” to form?
Rutile is the essential element that causes the star-effect in star sapphires. The more densely packed the rutile, the better the star. This effect or optical phenomena is known as “Asterism".
Asterism occurs when the light is concentrated into three rays that intersect at right angles to the direction of the needles, thus creating a six-legged star. Usually these stones only star in
sunlight or under strong indoor light (such as spotlight or halogen light). Of course, synthetic stars display asterism perfectly in all lights, which make them simple to detect.
How to determine the price of a star sapphire?
The value of star sapphires is basically influenced by two things:
(a) The strength and sharpness of the star,
(b) Intensity and attractiveness of body colour
Cutting:
All star sapphires are cut as medium to high domed-cabochons. This is necessary to display the star effect. Most star
sapphire cabochons are round or oval shaped. Usually the bottoms of the cabochons are left unpolished to prevent light from escaping from the gemstone. The star should be properly centered when the
gem rests on its base.
Colour:
Although star sapphires occur in a variety of colors, the supply of fine stones is always limited. Black star sapphires
which range from translucent to opaque are often very dark brown, green, or blue, rather than true black. Black stars are the most readily available and least expensive natural star stones. Green
star sapphires are rare and yellow or orange ones are very rare. It is extremely rare to find a star-sapphire with a sharp star and a bright blue body color. Also it must be noted that grayish
sapphires tend to have better stars than the blues.
Clarity:
Rutile (Silk), which is normally considered an inclusion, is what causes “the star-effect” in star sapphires. Hence star
sapphires can never be transparent.
Carat Weight (Size):
Normally, star sapphires are available in the sizes ranging from 1 carat to 15 carats. Large star sapphires are
extremely rare and are therefore very expensive.
Star Sharpness:
Each star should be complete and sharp, with no missing or broken legs. In a perfect star sapphire, each of the 6 rays
should reach the girdle.
Sources of Star Sapphire:
The finest blue star sapphires come from Mogok (Burma) and Srilanka. Kashmir in India used to be one of the most desired
sources of star sapphire but unfortunately the deposits have been depleted. As for black star sapphires, the most valuable are the golden-star black stars from Chanthaburi, Thailand. Other major
sources of Star Sapphires are India (Kashmir), Pakistan, Sri Lanka (Ceylon), Afghanistan, Vietnam, Tanzania, Malawi, Madagascar, Zimbabwe (Rhodesia), Kenya, Malagasy Republic, Brazil, Cambodia,
Australia and the United States (Montana, North Carolina). As of 2007, Madagascar leads the world in the mining of star sapphires.
Characteristics of Sapphires:
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Classification |
Mineral |
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Group |
Corundum |
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Molecular formula |
Al2O3 |
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Composition |
Aluminium oxide |
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Mohs Scale Hardness |
9 |
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Crystal Shape |
Trigonometric |
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Spectrum |
Blue, yellow, pink, white gamma |
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Atomic (Crystal) Structure |
Cross sectional |
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Refractive Index |
1.762–1.770 (0.008) Uniaxial negative |
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Density (Relative) |
2.65 - 2.68 |
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Light interaction |
Vitreous to semi-transparent |
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Fluorescence |
Blue none; colorless orange-yellow, violet |
Black Star Sapphires:
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| Black Star Sapphires with a Golden Star | A Rare 12-ray Black Star Sapphire |
Next: Star Sapphire Myths, Legends & Beliefs | Buy Star Sapphires