Mushroom rhyolite is a species of jasper or rhyolite, usually a green matrix with bubbles of gray that when cut produce images of mushrooms.

I have exactly two pieces of mushroom rhyolite, both of which originated from the same source. One of the pieces came locked into the vice of a slab saw I bought from an ad on Craigslist. The other piece was tossed in because the seller couldn't make change for a 20.

I'm told the desert out toward Wickenburg is littered with mushroom rhyolite. That's a big area so I'm not real sure where to start looking.