First off: “Wendy is correct – the price of synthetic quartz vs. natural quartz is pretty much the same. Since both materials are very common in the gem market with almost no one willing to pay a premium for advance testing, there is no financial incentive to figure out which is which.”
NO: Synthetic amethyst is MAXIMUM $1ct (if you want 20000cts, you can get it as cheap as $0.30ct, probably less). Fine quality Uruguayan amethyst starts at about $15-$20 USD/ct, and that is for parcels, dealers in NYC are selling the best qualities for $40-$50ct for single gems.
Amethyst prices have been rising (like all gems), a friend said to me about a decade ago: “We are going to find out how much synthetic amethyst is around when it gets expensive enough for people to start getting certs on it” Well, we are getting there already (disclosure, this is my site): https://skyjems.ca/collections/certified-gemstones/amethyst
Now, onto detecting natural from synthetic… Almost all natural amethyst has at least SOME zoning to it.
SOME synthetics do, but, the zoning is perfectly straight and obviously not natural. Also, no banding of color.
So… the quick and dirty way to check is put it in a white bowl with water in it, table down. If there is no zoning, you have a ‘more testing required’ situation. If there is ‘flowing’ zoning through the gem, you are almost certainly good.