General Information
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What are Star Rubies? |
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What caused the “star-effect” in Star Rubies?
Star-effect or "asterism" is caused by the dense inclusions of tiny fibers of rutile (also known as "silk"). The stars are caused by the light reflecting from needle-like
inclusions of rutile aligned perpendicular to the rays of the star. However, since rutile is always present in star rubies, they are never completely transparent. In fact, star ruby is one of those
few gemstones which actually require inclusions (i.e. rutile).
Are Star Rubies Rare?
Today, out of every 100 rough corundum (ruby and sapphire) mined; only three will have stars apparent after being cut into cabochons. Out of these three, one will have a poor color but a good star;
one will have a poor star but a good color and only one out of hundred will have both a good star and a good color! Most original sources of star rubies such as Mogok (Burma) have run out of
supplies. Worldwide production today is yielding a very small quantity of fine stars (especially in sizes above 5 carats). Star rubies are becoming rare as most rough today is cut into faceted stones
after heating instead of being cut into cabochons to display the star. Till the 1960’s star rubies fetched more prices than faceted rubies!
How to determine the price of a star ruby?
The value of Star rubies is basically influenced by two things:
(a) The strength and sharpness of the star,
(b) Intensity and attractiveness of body colour
Cutting:
Cutting is very important to exhibit the star effect in ruby. They need to be cut into medium to high, domed cabochons to get the perfect star effect. The cabochons must be round or oval-shaped. The stone should not be too flat on the top or too heavy on the bottom. Many a times, bottoms of star rubies are kept unpolished so that the light is trapped inside the gemstone.
Colour:
Generally rubies are red. But star ruby is usually not red. Most star rubies are available in pinkish-red, purplish-red or purplish-brown colour. The distribution of colour is often uneven, in
stripes and spots. A red ruby with a perfect star is very rare and costly. As a general rule, pink star rubies have the best stars.
Clarity:
As mentioned earlier, due to the presence of rutile (silk) star rubies are never transparent. Most natural star rubies found are translucent and opaque (mostly opaque).
Carat Weight (Size):
Normally, star rubies are available in the sizes ranging from 1 carat to 15 carats. Fine star rubies of large sizes are extremely rare and cost a lot of money.
Star Sharpness:
The star should be sharp (not blurry) and silvery / milky white. The best way to test the sharpness of the star is to look at the star ruby in sunlight with the dome facing the sun. All six prongs
should be straight and equally prominent. The complete star should be centered in the middle of the gem, but should also be able to glide effortlessly around the cabochon.
Sources of Star Ruby:
Most rough rubies that can be cut into stars are mined from Burma (Myanmar), Srilanka, India, Africa, Vietnam, Thailand, Afghanistan, Pakistan, Australia, Cambodia, United States. The most commonly
available Star Rubies are usually from Africa and Indian.
Characteristics of Ruby:
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Classification |
Mineral |
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Species |
Corundum |
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Chemical Composition |
Aluminium oxide with chromium, Al2O3::Cr |
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Mohs Scale Hardness |
9.0 (Second Hardest after Diamond) |
| Colour | Varying Red |
| General Clarity | Semi-Transparent to Opaque |
| Refractive Index | 1.762-1.778 |
| Specific Gravity | 3.97 to 4.05 |
| Birefringence | -0.008 |
| Colour of Streak | White |
| Absorption Spectrum | 694, 693, 668, 659, 610-500, 476, 475, 468 |
| Toughness | Excellent |
Some Pictures of Star Rubies:
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Burmese Star Ruby |
Sri Lankan Star Ruby |
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Indian Star Ruby (Rough) |
Rough Star Ruby |
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From Rough to Polish |
More Star Rubies |
