The special light reflections are generated by fine crystal fibers or needles, which are embedded in the host crystal in question and meet at a point if they are ideally distributed. Fine hollow channels in the stone are also able to create the star effect. The more evenly the fibers, needles or hollow channels are arranged, the more harmonious the star of light appears. Depending on the crystal system and class of the mineral concerned , there are 4, 6, 12 and 24-pointed stars. In addition, circular asterism can occur in rose quartz .
Asterism is preferred with sapphire and ruby , the varieties "star sapphire" and "star ruby" have therefore been named after this effect. Asterism can also be created in synthetic gemstones . However, while even the most beautiful natural star shine has a slightly irregular shape, artificially produced asterism is characterized by its (too) great perfection. The individual fingerprint of nature is missing. The asterism is particularly emphasized by the appropriate cut ( cabochon cut ).
More common and above all affordable stones with asterism form the so-called "star grenade " from the mineral group of the grenade . Grenades form asteric stones relatively rarely, but the locally abundant grenades are very similar in every deposit. There are also spinels, aquamarines and moonstones with asterism.
The asterism can usually only be seen when a more or less punctiform light source is pointed at the crystal. In evenly lit rooms with multiple light sources, the crystals appear less attractive.
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- Mineral Atlas: Asterism
- The large art lexicon by PW Hartmann. Asterism. In: beyars.com. BeyArs GmbH, accessed April 20, 2018 .
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- Asterism (star effect, star shine). In: renesim.com. RENÉSIM GmbH, accessed on April 20, 2018 .
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