Aventurescence: Light-Reflecting Inclusions That Produce a Bright Flash
Sunstone from Oregon

Aventurescence is an optical reflectance effect seen in certain gems. The effect amounts to a metallic glitter, arising from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body colour.

The aventurescent effect is a sparkling or glittering effect caused by the reflection of light from tiny disc-like inclusions, typically composed of mica, copper or hematite.

In aventurine quartz chrome-bearing fuchsite produces a green stone, and various iron oxides produces a red stone.

Aventurine quartz is the best-known of aventurescent gems (and the reason why the phenomenon was named aventurescence). Even so, aventurescence can actually occur in a variety of other gemstones too, including various feldspars such as sunstone and andesine-labradorite. A variety of obsidian known in the trade as 'gold-sheen obsidian' is also known to exhibit an extremely attractive aventurescence.

The words aventurine and aventurescence derive from the Italian "a ventura," meaning "by chance." This is an allusion to the chance discovery of aventurine glass or goldstone at some point in the 18th century. Goldstone is still manufactured today as an artificial imitation of later discoveries aventurine quartz and aventurine feldspar (sunstone).

Aventurescence: Light-Reflecting Inclusions That Produce a Bright Flash
Oregon sunstone is unique for its copper content.