In a previous article we discussed the sapphires which use in our claddagh rings. In this article I would like to provide more detail on a very desirable and some what rare optical effect present in some sapphires and rubies. This effect is asterism also known as the star effect whereby a star appears inside the gemstone.
In order for this effect to be best displayed the sapphire or ruby would be cut in the cabochon cut. For this reason it is not available in the heart cut and thus is not used in the sapphire claddagh ring. The effect is due to fine parallel fibers and crystals inside the gemstone. In fact three sets of them lying along the crystals lateral axes and intersecting each other at 60 degrees.
Some Thai star sapphires produce a 12 point star. A variety of gems display the star effect. The best asterism is displayed in rubies and sapphires as a 6 point star. It appears in rose quartz, diopside. It also appear in garnets as a 4 point star.
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