Another reason is because amethyst while still a bargain price compared to other gem species has steadily gained in value to where it is no longer considered so much a "semi precious gem" this makes it worth faking.
Cheap amethyst rings with poorly cut fake stones abound as do more expensive and larger amethyst look alike's.
The bottom line is that excellent quality custom cut amethyst's can be bought with verified natural origins and many times with a picture of the actual rough material the stone was cut from,of course you will only get this from small artisan cutters in the United states,Canada,Australia and some European countries.
So if you're a quartz lover and happen to be looking for that special amethyst don't be duped into buying a cheap synthetic but rather purchase a finely crafted natural stone from an artist and have something you would be proud to pass on as an heirloom.
