light falls on these stones, a star effect is visible (known as asterism).
Sri Lanka is the best known source for star sapphires and star rubies. Star
sapphires range in colour from grey to bluish-grey and from medium blue to
medium dark blue. The very slightly purplish medium dark blue is the best
colour grade for star sapphires. Star rubies range from light pink-red to
purple-red through deep purple-red. The intense red star rubies are
extremely rare. A good quality star stone should have a high degree of
transparency and a well defined star with no weak or missing rays. It should
be reasonably clean and in the face-up position, no distracting inclusions
or cracks should be seen. There should be no excess weight at the bottom of
the stone.
Star sapphires and rubies are hard stones (9 on the Moh's scale), which can
take a high degree of polish and retain the shinefor a long time. The
special optical phenomenon of a well-defined six-ray star is a fascinating
sight. The wearable qualities of the star stones make them suitable for
men's rings.
Varieties - Star sapphire, Star Ruby
Treatments - Heat treatments. Treatment of Ruby and Sapphire stones are
permanent.
History - One of the world's finest large example, the Rosser Reeves Star
Ruby, was mined in Sri Lanka. The Star of Sri Lanka (wrong uses as India),
at 563 carats, is the largest and most famous star sapphire in the world.
Formed some 2 billion years ago, it was discovered, allegedly more than 300
years ago, in Sri Lanka. Industrialist and financier J. P. Morgan presented
the sapphire to the American Museum of Natural History in 1900. Today, the
Star of Sri Lanka (India) and the Rosser Reeves Star Ruby resides in the
Morgan-Tiffany Collection in the American Museum of Natural History in New
York City.
The presence of the mineral rutile in the Star of India gives the stone its
milky quality. This also yields the star effect, as tiny fibers of the
mineral, aligned in a three-fold pattern within the gem, reflect incoming
light in the star pattern. This effect is known as asterism, and, along with
color, is one of the characteristics that makes star sapphires so highly
prized. Such stones are polished in the domed shape you can see here, called
a cabochon, to best reveal the star, which moves with changing angles of
illumination and observation.
Star sapphires and rubies are hard stones (9 on the Moh's scale), which can
take a high degree of polish and retain the shinefor a long time. The
special optical phenomenon of a well-defined six-ray star is a fascinating
sight. The wearable qualities of the star stones make them suitable for
men's rings.
Star sapphire is the result of reflection of light from fine, oriented,
rutile needles. Like star ruby, star sapphires may be heat treated to high
temperatures to dissolve the rutile and produce blue sapphires of good
clarity. Such has been the recent fate of much of the Sri Lankan Geuda
material that might have otherwise been uncutable (too dark and/or cloudy).
Unfortunately, some reports state that much of the good star material is now
suffering the same fate. The same characteristics apply to good star
sapphire as to star ruby (see above). The best body color is an intense pure
blue, but such natural stones are rare and one more frequently encounters
blues that are more gray. Fine blues are more translucent than even good
gray-blues and are cabbed thicker as a result. Such stones may appear to be
"overweight" with bulky bases, an important consideration when paying by
weight but a necessity to maintain a deep blue color. This is not the case
for average blue stones, however, and you should not pay for excess weight
unnecessarily.
Choosing a Star Stone
Star Gemstones have long been coveted for their beautiful and mysterious
optical effects. Glance at a star gemstone and you will see four, six or
even twelve rayed stars silently gliding across the gemstone's surface.
This intriguing optical phenomenon is unique to the world of gemstones.
Technically known as the "Asteric Effect", it is caused by sets of parallel
needle-like inclusions of foreign minerals. Sometimes known as "silk", the
needles are oriented in all or some of the directions of the crystal
structure. These needles are responsible for reflecting intersecting bands
of light back to the eye.
Sri Lanka and Burma are the world's top producing Star Ruby and Sapphire
locations. Generally, Sri Lanka for Blue and Fancy Colors, Burma for Red,
Blue and Fancy Colors. However, Star Rubies and Sapphires are found in
virtually all Ruby and Sapphire producing locations. Ranging in quality from
grayed-out colors with indistinct stars, to beautiful color hues with bright
and distinct stars, prices can range from just a few dollars to many
thousands.
The value of star rubies and sapphires are influenced by two factors: the
intensity and attractiveness of the body colour and the strength and
sharpness of the star. All six legs should be straight and equally
prominent. Star rubies rarely have the combination of a fine translucent or
transparent colour and a sharp prominent star. These gems are valuable and
expensive.
Judging the quality and value of star gemstones is best done underneath
singular light sources. Singular light sources such light bulbs, candles,
direct sunlight, spotlights and penlights are ideal to judge star gemstones.
Diffused illumination, such as fluorescent strip lamps, greatly blurs the
effects leading you to make an erroneous conclusion. Avoid making any
judgments underneath diffused lighting. At Thaigem.com all our Star Gems are
selected, described and photographed under single light sources.
The Distinctiveness Of The Star: The star of a gemstone should ideally be
well contrasted against the body color of the gem. The more distinct the
star, the better the quality. The Length & Straightness Of Each Ray:
Straight rays that reach almost girdle-to-girdle are the most desirable and
valuable. In reality, perfectly straight girdle-to-girdle rays are rare.
Color: As always, color is a deciding factor with gemstones. A gem should
have bright vivid coloration that is free from dull overtones and is evenly
distributed across the surface of the Gem. The Cut & Star Position: The
outline of the gem should ideally be regular and well cut around the girdle.
When you look at the star, it should appear to sit in the middle of the gem,
not to one side. Stars that sit on top of the gem are most desirable. Carat
Weight: As always, carat weight affects the per carat price. Higher weights
are more rare than smaller weights and thus command a higher premium per
carat.
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