GeoEvelyn has declared this Geology-Picture-A-Day Week and I thought I’d join in. Mostly since I need a couple of things identified.
Found this chunk of aa (rubbly basalt) in the roof of a collapsed lava tube right next door to where we stayed on the Big Island of Hawaii. What are the growths/precipitates on the aa surface? They look like tiny little mushrooms but are actually crystalline. American nickel for scale.