I’ll start the week with the obligatory, purchased deskcrop of amethyst crystals. In this case, these were a gift from my parents a couple of years ago, and like many of my deskcrops they’ve seen double duty as a teaching specimen on occasion.
In nature stores and rock shops I’ve seen many samples like this (some much larger). They seem to often list a provenance as Brazil, though I’m not certain my sample ever included this information. Wikipedia tells me “amethyst is produced in abundance from the state of Minas Gerais in Brazil where it occurs in large geodes within volcanic rocks” and I have little reason to doubt just such an origin for this sample.
One thing I have often idly wondered about was the origin of the teal colored substrate on which the amethyst crystals are growing. It doesn’t appear to be unaltered basalt, though I could imagine that it is some sort of altered variety of that rock type. Any geologist want to take a stab at explaining the makeup of that teal material?