My amethyst was not amethyst

Bought a gorgeous 'amethyst' cluster at a market last spring and brought it to mineralogy lab today because I was proud of it. My lab partner (geology major, very gentle about it) did a quick hardness check and a look under the loupe.

Dyed agate. Very purple. Not even slightly amethyst.

I was embarrassed for about an hour and then kind of delighted, because now I actually know how to tell. Real quartz scratches glass, amethyst color usually sits in zones rather than pooling in the cracks, and if it looks like grape soda, it probably is. The agate is staying on my windowsill anyway. It didn't lie to me. The seller did.