(n.) A crystalline rock, consisting, like granite, of quartz, feldspar, and mica, but having these materials, especially the mica, arranged in planes, so that it breaks rather easily into coarse slabs or flags. Hornblende sometimes takes the place of the mica, and it is then called hornblendic / syenitic gneiss. Similar varieties of related rocks are also called gneiss.

aa abyssal rock basalt bedrock block lava brash breccia conglomerate crag druid stone festooned pahoehoe granite igneous rock lava limestone living rock magma mantlerock metamorphic rock monolith pahoehoe pillow lava porphyry pudding stone regolith rock ropy lava rubble rubblestone sandstone sarsen schist scoria scree sedimentary rock shelly pahoehoe stone talus tufa tuff