I have read that amethyst was quite valuable at one time. Then
huge Brazilian deposits were found. Does anyone have data on
historic amethyst prices?
I do not have historical data, but it is true that amethyst was
highly desired gemstone at one time. Decline in price is not due to
Brazilian deposits, but development of lab-grown quartz which is not
easy to tell apart from natural even for gemologist. So prices
declined to the level of lab-grown material.