Aventurine

Aventurine is a variety of quartzite (metamorphosed sandstone) that contains platy mineral inclusions which create a sparkly, shimmering effect called aventurescence. In green aventurine - by far the most common variety - the sparkle comes from tiny flakes of fuchsite, a chromium-rich mica.

The stone forms when quartz-rich sandstone is subjected to regional metamorphism, recrystallizing the quartz grains while trapping existing mica flakes in alignment. These aligned, reflective platelets catch and reflect light, producing the characteristic glittering effect.

Different inclusion minerals create different colors: fuchsite (chrome mica) for green, hematite or goethite for red-brown, and dumortierite for blue (though blue aventurine is rare and highly sought after). The degree of aventurescence varies from subtle to dramatic depending on the density and size of the inclusions.

Aventurine is identified by its aventurescence - the sparkly, glittering shimmer visible when light hits the internal platy inclusions. This distinguishes it from jade (no sparkle), amazonite (different mineral, no sparkle), and dyed quartzite (which may have color but no aventurescence).

At Mohs 7, aventurine is hard and durable. It has a slightly granular texture compared to the smooth, even surface of jade. The sparkle is most visible on polished surfaces viewed at certain angles - rotate the stone under direct light to see it.