block: a solid rock fragment greater than three inches in diameter that is ejected from a volcano during eruption

bomb: a partially molten lava fragment greater than three inches in diameter that is ejected from a volcano during eruption; many bombs acquire rounded aerodynamic shapes as they fly through the air

dacite: one of the most common rock types associated with enormous Plinian-style eruptions; dacite lava consists of 63 to 68 percent silica, erupts at temperatures of between 800 and 1000°C, and is often light gray in color after cooling

effusive eruption: an eruption characterized by an outpouring of lava onto the ground (as opposed to the fragmentation of lava into the air during violently explosive eruptions)

fumarole: vents from which volcanic gases escape into the atmosphere; these usually occur along fissures or on the surface of lava flows that have cooled enough to have a crust

hornito: a small cone that forms on the surface of a lava flow when hot lava is forced up through an opening in the cooled surface of a flow and accumulates

inclusion: a rock or liquid that is enclosed in another foreign kind of rock or mineral

pumice: a light, porous volcanic rock that forms during explosive eruptions; all types of magma form pumice

pyroclastic flow: a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 63 miles/hour or more

reticulite: a light, porous volcanic rock that forms during explosive eruptions

rhyolite: rhyolite lava erupts at 700 to 850°C and contains a silica content of over 68 percent; it can also include the minerals quartz, feldspar, and biotite, which harden with a glasslike texture

scoria: a bubbly and glassy lava rock high in iron content

xenolith: a rock fragment that is foreign to the mass in which it is embedded