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asterism (star effect, star shine)

Asterism is the name for an extraordinarily beautiful and mysterious optical phenomenon that is very rarely found in nature. It describes the star-shaped sparkle of a gemstone when rays of light are reflected from a crystal. The other names star effect and star shine, as well as the term asterism itself (Latin for constellation), already reveal that the effect is a star-shaped light phenomenon on gemstones .
Sternsaphire Star Sapphires – Sapphires with Asterism

The Asterism – An Enchanting Light Figure

Responsible for the formation of an asterism are tiny inclusions such as needles and fibers in the gemstone, which are only visible under a microscope. These must be collected in several bundles arranged in different directions so that the light entering the crystal can be reflected in the shape of a star. The prerequisite for the asterisms to have a beautiful and even shape is that the needles are evenly arranged. If this is not the case, the stars are distorted. If an asterism is too perfect, this is an indication that you are dealing with an artificial gemstone. An asterism is only visible if the gemstone is cut into a cabochon , i.e. polished smooth and curved outwards. A point-shaped incidence of light, such as that produced by the sun or a light bulb, is also important. If a gemstone with an asterism is moved in such a light source, the star shine glides over its surface.

gemstones with asterism

Sapphires and rubies can exhibit particularly beautiful six-pointed asterisms, making star sapphires and star rubies highly sought after. The four-pointed star garnet and the twelve-pointed star diopside are considered even rarer. This asterism also occurs in spinels, aquamarines, and moonstones .