- A Hard Building Stone - extremely hard rock - Igneous rock - Igneous rock derails train, e.g. - Quartz rock - Type of rock - A crystalline, granular rock, consisting of quartz,
feldspar, and mica, and usually of a whitish, grayish, or flesh-red
color. It differs from gneiss in not having the mica in planes, and
therefore in being destitute of a schistose structure.