Laura Norlin
Quiz 4 (for Week 5 Tuesday 2/11/03) (words from Key Terms section of
Chapter 6, Marshak, 2001, pp. 160)
Aphanitic, Batholith, Country Rock, Dike, Extrusive, Intrusive, Laccolith,
Pegmatite, Phaneritic, Phenocrysts, Pluton, Porphyritic, Pyroclastic
Flow, Sill, Tuff, Xenoliths
Aphanitic- A textural term for fine-grained igneous rock.
Batholith- A vast composite, intrusive, igneous rock body up to several hundred
km long and 100 km wide, formed by the intrusion of numerous plutons in the
same region.
Pluton- An irregular or blob-shaped intrusion; can range in size from tens of m
across to tens of km across.
Country rock (wall rock) - The preexisting rock into which magma intrudes.
Xenolith- A relict of wall rock surrounded by intrusive rock when the intrusive rock
freezes.
Dike-A tabular (wall-shaped) intrusion of rock that cuts across the layering of
country rock.
Pegmatite- A coarse-grained igneous rock containing crystals of up to tens of
centimeters across and occurring in dike-shaped intrusions.
Extrusive igneous rock- A rock that forms by the freezing of lava above ground,
after it flows or explodes out (extrudes) onto the surface and comes into contact
with the atmosphere or ocean.
Intrusive igneous rock- Rock formed by the freezing of magma underground.
Laccolith- A blister-shaped intrusion that forms when sills dome upward.
Sill- A nearly horizontal table-top-shaped tabular intrusion which injects between
the layers of country rock.
Phaneritic- A textural term used to describe coarse-grained igneous rock.
Phenocryst- A large crystal surrounded by a finer-grained matrix in an igneous
rock.
Porphyritic- A textural term for igneous rock that has phenocrysts distributed
throughout a finer matrix.
Pyroclastic rock- Rock made from fragments blown out of a volcano during an
explosion that were then packed or welded together.
Tuff- A pyroclastic igneous rock composed of volcanic ash and fragmented
pumice, formed when accumulations of the debris cement together.
Ash flow- An avalanche of ash that tumbles down the side of an explosively
erupting volcano.