Dacite   This is an extrusive igneous rock comprised of feldspars, quartz, and hornblende or biotite mica. It is chemically very similar to the granitic rock at the Graniterock AR Wilson Quarry, but because it was extruded by a volcano and cooled relatively quickly, it is much more fine grained. Rocks that are intrusive and cool slowly (over millions of years) can grow large crystals, like Graniterock AR Wilson granitic rock. Country Cottage