<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 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>
smooth glassy rock that forms when lava cools
smooth glassy rock that forms when lava cools
Volcanic rocks
Volcanic rocks