Green crystalline quartz is uncommon in nature; however the top specimen is of natural green quartz from McDougalls Well, New South Wales, Australia, while the bottom is created by heating regular amethyst. In the case of heat treatment, some or all of the stone may turn green, and if some purple remains, it is sometimes marketed as ‘Amegreen’ or ‘Green Amethyst’ in stores.
Confusingly, the name ‘Prasiolite’ is also used to refer to both the heat treated and natural green quartz. There is one location in Namibia where sort-of-greenish Amethyst occurs, to make things even more complicated; but the tumbled stone in the lower image is stated to be from India.
An in-depth discussion on the issue can be read here:[link]
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