Prasiolite: "Green Amethyst"?

Prasiolite:  "Green Amethyst"??

I often see "green amethyst" jewelry (and loose stones) for sale on etsy, and elsewhere on the internet.  It seems popular, and is a little pricey.  I've wondered about the name "green amethyst" though---I mean, do we call citrine "yellow amethyst"?  Or clear quartz, "clear amethyst"?   It seems sort of weird... so I did a little research.

Untreated Amethyst

Since amethyst is, by definition, the violet to purple shade of quartz, there is really no such thing as green amethyst!  Some gemstone varieties are simply defined by their distinctive color, such as emerald, or ruby, or ametrine.

Why do people sell, and buy, something called "green amethyst"? What is it? Where does it come from? Does it have anything to do with amethyst?

What people are selling and buying is actually something known by gemologists as prasiolite. The name comes from the Greek word for "leek-green." Prasiolite is a golden green quartz, somewhat similar in color to peridot, or lemon quartz!

Here's the most interesting thing:  there is no such thing as "natural" or "untreated" prasiolite!  Prasiolite (or green quartz) starts as amethyst, or pale yellow quartz, and is heated until the green color is achieved.  However, not all amethyst or yellow quartz can be heated to produce prasiolite. According to gemological sources, only quartz from the Montezuma deposit in Minas Gerais, Brazil can be heated to produce prasiolite. The quartz is heated to about 500 degrees centigrade to produce the light golden-green color.

Unfortunately, the color is not stable and is known to fade when exposed to strong sunlight!

Synthetic Green Quartz

Some of the "prasiolite" on the market is actually synthetic quartz or glass!  Whenever you see a deep minty green or blue-green stone that is called "green amethyst" it is NOT prasiolite at all!  These stones in the artificial greens are actually synthetics.

Are there any naturally-occurring green quartz stones?

Yes.  There are members of the chalcedony family that are natural, translucent green stones:  chrysoprase and aventurine.  Chrysoprase is a natural stone that varies in color from apple green to deep green.  Aventurine is a natural green stone with glittery mica inside!

So then why is Prasiolite sold as "Green Amethyst"?

Sadly, the answer is perhaps greed, or what I like to call, "creative marketing".    
Since amethyst is the most valuable gem in the quartz family, calling this green heated quartz "amethyst" is just an attempt to "elevate" prasiolite and charge a premium for the stone. I guess that, if it's genuine prasiolite, it began as amethyst and then is heated to achieve the green color, it's not a complete fabrication, but it is a stretch!