Volcanic Rock

High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! Volcanic rock is an igneous rock of volcanic origin. Volcanic rocks are usually fine-grained or aphanitic to glass in texture. They often contain clasts of other rocks and phenocrysts. Phenocrysts are crystals that are larger than the matrix and are identifiable with the unaided eye. Rhomb porphyry is an example with large rhomb shaped phenocrysts embedded in a very fine grained matrix. Volcanic rocks often have a vesicular texture caused by voids left by volatiles escaping from the molten lava. Pumice is an example of explosive volcanic eruption. It is so vesicular that it floats in water.