My watch list

Asterism (gemmology)

This article is about the characteristic in some gems. For other uses, see Asterism

This article or section relies largely or entirely upon a single source.
Please help improve this article by introducing appropriate citations of additional sources.

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. Star sapphires and rubies get their asterism from the titanium dioxide impurities (rutile) present in them.^[1]

Additional recommended knowledge

Don't let static charges disrupt your weighing accuracy

What is the Sensitivity of my Balance?

How to ensure accurate weighing results every day?

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.

References

^ Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford: Oxford University Press, pp. 451 – 53. ISBN 0-19-850341-5.

v • d • e Common jewelry materials
Precious metals:	Gold · Silver (Sterling silver) · Platinum · Palladium
Gemstones:	Diamonds · Rubies · Emeralds · Sapphires · Amethyst · Opals · Topaz · Aquamarine · Tanzanite · Alexandrite
Others:	Amber · Pearls