Most of the Green Amethyst on the market today comes from Brazil. It's Amethyst that has been heated to arrive at the gorgeous mint color. We purchased over 100 of these crystals and faceted one of them into this large 10x8mm rectangular shaped gemstone weighing 3.1 carats.  We set in a Sterling Silver Pendant.
 
Just as an aside, naturally occurring mint green quartz is called Prasiolite, and most of these crystals come from one small mine in the northern Brazilian State of Minas Gerais. The color is caused by naturally occurring radiation over millions of years.