1. (n.) A soft or porous stone formed by depositions from water, usually calcareous; -- called also calcareous tufa.

2. (n.) A friable volcanic rock or conglomerate, formed of consolidated cinders, or scoria.

aa abyssal rock bedrock block lava brash breccia conglomerate crag druid stone festooned pahoehoe gneiss 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