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Star Stones

Star stones are part of a special group of phenomenal gems in the world of gemstones. These stones exhibit special optical phenomena, including asterism (star effect), color gradation (cat's eye effect) adularescence (flickering light) and iridescence (rainbow effect).

star ruby
bharany star ruby
rosses reeves star ruby stone

Since these phenomenal gemstones are relatively rare they attract the attention of the collectors. In some cases, all or most of gems belonging to a particular species exhibit the phenomenon, as well as most moonstones exhibit adularescence for example. But in other cases the optical effect is seen only occasionally in a certain type of gemstone and these rare cases are of particular interest to the collectors.

Asterism or star effect is an example of an optical phenomenon that is rarely found in a small number of precious stones cut as cabochons. The most famous examples are the star sapphire and star ruby. But asterism can occur also in moonstone, quartz, spinel, citrine, diopside, emerald, garnet and chrysoberyl.

The reason that asterism is so rare is that it is necessary the gem to contain inclusions of rutile needles that are arranged in a way as to reflect the light in a shape with many rays forming a star. Usual rule for gem of better quality is the fewer inclusions, the better. But in this case, the value is increased by the appropriate type of inclusions.

The value of a star gemstone depends on the purity and clarity of the star. In principle the star should be evaluated by a individual source such as a flashlight for example. Usually it is very difficult to see the star in the scattered light. Moving the light back and forth would make the star to move along the surface of the stone. Rays of the star must be evenly distributed and relatively straight. The most common stars have 4 and 6 beams, although there are some with 12 beams.

The color is also very important in star gems. Ideally the color should match the “non-star” variety of stone  but rutile presence weakens the color. So in the best case there is enough rutile to form a clear star while minimizing the effect on the color.

Burma and Sri Lanka are the most important sources of star rubies and star sapphires. Thailand is famous for its black and gold star sapphires, which are found only in the province of Chantaburi . Some star sapphire are produced by diffusion treatment when sapphire is heated with a layer of titanium dioxide which diffuses into corundum and forms rutile needles.

First synthetic star sapphires were produced in the late 40s of the 20th century. At the moment they are manufactured in Japan by "Nakazumi Earth Crystals". Synthetic gemstones have perfect color and the star is so bright and correct that it looks like it is painted on the stone.

sapphire indian star

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