I found an interesting rock while driving some back roads in northern Nevada a couple of weeks ago. It was lying next to the two-track, and I noticed it because it had a greenish tint. The country rock there is either rhyolite, or basalt, and dark in color. This rock is definitely an anomaly. It may be a lamproite tuff, or maybe it's simply a form of rhyolite. It is scratchable with a knife blade, but not easily. A couple of drops of muriatic acid had little noticable effect. The main rock was about 10" across. The piece in the pics is about 3" x 3" x 5". If anybody can help, I'd be grateful.
Jim