you won't make yourself a name if you follow the rules

so, totally unrelated to anything, does anyone know of resources comprehensible by non-geologists (ideally freely available on the internet—academia.edu counts, as does JSTOR till the end of the calendar year—or at either of the nearby library systems I have cards for) on the sort of geology where amethysts are found?

(I am trying to look for my own worldbuilding resources on JSTOR but there are many and also I am less than thrilled with a search feature that finds me something on reproductive justice because the article has a hyphen and a line break in the word "undermining")