BASIC ROCK TYPES
- Igneous: The New - rocks which have
congealed from a molten mass. They can either be intrusive, like granite, or extrusive,
like basalt (lava).
- Sedimentary: The Used - rocks that
have formed by consolidation of organic or inorganic solid fragments, carried by,
suspended in, or droppped by wind, water, or ice and deposited in layers.
- Metamorphic: The Refurbished - a rock
formed from preexisting solid rock by mineralogical, structural, and chemical changes in
response to extreme changes in temperature, pressure, and/or shearing stress.
- The Rock Cycle
- how each rock type comes into existence, highlighting in which province each can be
- Please refer to the Geologic Time Table for
ages and descriptions of Eras (e.g. Paleozoic, Mesozoic), Periods (e.g.
Cambrian, Cretaceous), and Epochs (e.g. Pliocene, Miocene).
- Ma - mega-annum - a period of one million
- Ga - giga-annum - a period of one billion
- kilometer - a distance of 1000 meters, equivalent to 0.62 mile (where
one meter is equivalent to 3.3 feet).
allochthonous (Blue Ridge) - a rock that
was transported a great distance from its original deposition by some tectonic process,
generally related to overthrusting, recumbent folding, or gravity sliding.
anorthosite (Piedmont) - a visable crystalline plutonic rock
almost completely composed of plagioclase feldspar with minor amounts of pyroxene and
clastic sediments (Valley & Ridge) -
deposits of rocks or sediemts composed of clasts which have been transported from their
place of origin by mechanical agents.
crustal shortening (Blue Ridge) - a reduction in size of the
land area of the Earth's crust due to tectonic influences such as collisions with other
landmasses, resulting in mountain building (orogenies).
crystalline rock (Blue Ridge) - 1. Rock made up of minerals
in a clearly crystalline state. 2. Igneous and metamorphic rock, as opposed to sedimentary
dikes (Piedmont) - An intrusive rock body that is substantially
wider than it is thick. Dikes are often steeply inclined or nearly vertical.
escarpment (Blue Ridge, Coastal Plain) - a
cliff or steepslope of some extent, generally separating two level or gently sloping
areas, and produced by erosion or faulting. Also known as as a scarp.
fold and thrust belt (Valley & Ridge)
- a linear region that has undergone folding or some other form of deformation during
periods of mountain building
grabens (Piedmont) - a block of the earth's crust, generally
with a length much greater than its width, that has dropped relative to the blocks on
granitoids (Blue Ridge) - igneous rocks that have a
composition very similar to granite (quartz and alkali feldspar, with subordinate
plagioclase and biotite and hornblende).
granulite-facies metamorphism (Blue Ridge) - a group of
gneissic rocks characterized by a granoblastic fabric and formed by regional dynamothermal
metamorphic at temperatures above 650° and pressures of 3000-12,000 bars.
Grenvillian basement (Blue Ridge) - a complex of intrusive
igneous and metamorphic rocks emplaced during the Grenville orogeny one billion years ago.
Iapetan rifting (Blue Ridge) - over one
billion years ago, the landmasses which would one day become known as Africa and Europe
were attached to eastern North America. When they broke up, or rifted apart, the
Iapetus Ocean was formed where that Atlantic Ocean would be 900 million years later.
The Greek god Iapetus was the father of Atlas, namesake of the Atlantic.
imbricated (Piedmont, Valley & Ridge) - tabular masses that overlap one
another and are inclined in the same direction.
karst topography (Valley & Ridge) - a
landscape formed over limestone, dolomite, or gypsum, and characterized by sinkholes,
caves, and underground drainage.
kyanite (Piedmont) - Al2SiO5, a
valuable metamorphic mineral used commercially as heat sinks (e.g. spark plugs and porcelain). Its long-bladed blue
crystals are distinctive and give the mineral its name (Greek kyanos, blue). It is an indicator of
deep-seated, regional metamorphism of clay-rich sediments.
massif (Blue Ridge) - a massive block of
rock within an orogenic belt, usually more rigid than the surrounding rocks, and commonly
composed of crystalline basement or younger plutons.
metabasalts (Blue Ridge) - a metamorphosed basaltic rock,
also referred to as a greenstone.
monadnocks (Piedmont) - a remnant hill of resistant rock
rising abruptly from the level of a peneplain (any land surface changed almost to a plain
by erosion); commonly represents an outcrop of rock that has withstood erosion.
orogeny (Blue Ridge, Valley & Ridge) -
the process or processes of mountain formation, especially the intense deformation of
rocks by folding and faulting which, in many mountainous regions, has been accompanied by
metamorphism, invasion of molten rock, and volcanic eruption.
plutons (Blue Ridge) - a large igneous
transgressions (Coastal Plain, Blue Ridge)
- geologic evidence of landward extension of the sea often, but not always, characterized
by a sandstone grading into shale into carbonate sequence.