Tumbled green aventurine

Typically green, translucent to opaque, with a vitreous-to-waxy polish and occasional subtle mica sparkle; hardness about 6.5–7 Mohs, granular quartz crystal structure, no prominent cleavage, specific gravity about 2.6–2.7. The pictured material may also be green quartz or serpentine, as color and inclusions are not fully diagnostic from one image.

Usually metamorphic quartzite formed when quartz-rich sandstone recrystallizes; green color commonly comes from chromium-bearing fuchsite mica. Deposits are widespread, notably in India, Brazil, Russia, and Tanzania; geological ages vary by deposit.

Used for beads, cabochons, carvings, ornamental stone, countertops, and inexpensive gemstone items. Common tumbled pieces generally have modest market value.

Aventurine is named for aventurescence, the reflective glitter produced by inclusions, though this specimen shows little obvious sparkle. It is often confused with dyed quartz, serpentine, jade, or green glass.

Check for natural granular texture, mica glitter, quartz-like hardness, and lack of bubbles; it should scratch glass but not be scratched by a steel knife. Common tumbled value is about $2–$10; larger or especially attractive specimens may reach $15–$40.