Aventurescence

 

Aventurescence visible on a round piece of sunstone

 

Aventurescence is an optical reflectance that can be seen in certain gemstones.  It's best described as a metallic glitter that's caused by minute plate-like mineral inclusions which can be so numerous they can even influence the colour of the gemstone.  As light reflects off the inclusions at specific angles, a distinctive flash of light can be seen.

Aventurescence can also be seen in the minerals aventurine and sunstone and the word is also used to describe the effect that can be seen as light reflects off the flecks of copper embedded within the synthetic gemstone known as goldstone.