<Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (May 2011) </Td> </Tr> <Ul> <Li> Lava </Li> <Li> Tephra </Li> <Li> Volcanic bomb </Li> <Li> Lapilli </Li> <Li> Volcanic ash </Li> </Ul> <P> 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 . </P> <P> Volcanic rocks often have a vesicular texture caused by voids left by volatiles trapped in the molten lava . Pumice is a highly vesicular rock produced in explosive volcanic eruptions . </P>

Smooth glassy rock that forms when lava cools