What is Asterism in regard to jewellery?

Answer 1

Funny that you should ask this, I looked up this question about a week ago myself.

In gemmology, an asterism is an optical phenomenon displayed by some rubies, sapphires, and other gems of an enhanced reflective area in the shape of a "star" on the surface of a cabochon cut from the stone.

A distinction can be made between two types of asterism:

* Epiasterism, such as that seen in sapphire and most other gems, is the result of a reflection of light on parallel arranged inclusions inside the gemstone.
* Diasterism, such as that seen in rose quartz, is the result of light transmitted through the stone. In order to see this effect, the stone must be illuminated from behind.