rhyolite

A fine-grained extrusive volcanic rock, similar to granite in composition and usually exhibiting flow lines.

The name given by Richthofen to certain rocks occurring in Hungary which resemble trachyte, but are distinguished from it by the presence of quartz as an essential ingredient, and also by a great variety of texture, showing more distinctly than rocks usually do that the material had flowed while in a viscous state.

A quartzose trachyte, an igneous rock often showing a fluidal structure.

An igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture.

very acid volcanic rock