Pumice is an example of extrusive igneous rock. The word extrusive means that the magma was forced onto the earth's surface and cooled in a matter of hours. Granite is an example of intrusive ...

Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidifies and can form extrusive igneous rocks or intrusive igneous ...

According to the seismologists, this suggests that entire oceanic slabs – up to 62 miles (100 kilometers) thick – carry significant amounts of the extrusive igneous rock as they descend ...