Radial, star-like crystal found on an unknown host rock. Guatemalan Highlands. Huehuetenango. I've seen these very rarely and had just assumed they were organic, but these pictures (to me) look like crystal formations. Any guesses? Carbonate filling in a cavity from old organic matter, perhaps? Or a different mineral altogether?
Robert, The radiating crystals could be any number of secondary minerals, crystallized in a joint crack. Erik has suggested a phophate . . . one way to check that is to drop some warm HCl (moderate concentration) on one of them. If it is a phosphate, it should dissolve. Alfredo has suggested strontianite, which will also dissolve in HCl. Try hitting the spot treated with HCl with the flame from a gas torch. If you get a scarlet flash, strontium is present. Might work with vinegar instead of HCl, I am not sure.
Edited 1 time(s). Last edit at 05/19/2017 05:42PM by Donald B Peck.