Just a SWAG. From the color and crystal habit it looks like native sulfur growths and concretions to me. If so, the crystals should be soft and scratch easily with a nail or knife blade. You can also test (in a well ventilated area!) by crushing and burning a small sample. It should burn with a distinctive blue flame and an unpleasant "rotten-egg" smell. That will be sulfur-dioxide and/or hydrogen-sulfide gas, so don't overindulge.