Ball bracelet 10mm from Aventurine from India.

Aventurine or aventurien is a green to red-brown colored variety of the mineral quartz. This gemstone usually occurs in the green and cut variant. Aventurine has a hardness of 7 and is found in Russia, the Urals and China. Aventurine, like many other varieties of quartz (for example amethyst and rose quartz), is cut so that it can be used as jewelry. The chemical composition of aventurine is SiO2 + KAl2(OH,F)2 / AlSi3O10 + Cr. The Ancient Greeks sewed aventurine into a warrior's clothing to preserve his courage, ambition and optimism.