Geology Reference
In-Depth Information
aquifer
A rock mass that readily stores and conveys
groundwater and acts as a water supply.
augite or other pyroxenes, and, in some basalts, olivine.
The fine-grained equivalent of gabbro.
aragonite
A form of calcium carbonate, dimorphous
batholith
A large and deep-seated mass of igneous
rock, usually with a surface exposure of more than
100 km
2
.
with calcite.
arête
A sharp, knifelike divide or crest.
bauxite
A pale-coloured earthy mix of several hydrated
aluminous (Al
2
O
3
n.H
2
O) minerals. The chief ore of
aluminium.
argillaceous
Referring to, containing, or composed
of clay. Used to describe sedimentary rocks containing
clay-sized material and clay minerals.
bedrock
Fresh, solid rock in place, largely unaf-
fected by weathering and unaffected by geomorphic
processes.
arkose
A coarse-grained sandstone made of at least
25 per cent feldspar as well as quartz.
arroyo
In the south-west USA, a small, deep, flat-
floored gully cut by an ephemeral or an intermittent
stream.
Bernoulli effect
The reduction of internal pressure
with increased stream velocity in a fluid.
biogeochemical cycles
The cycling of minerals or
organic chemical constituents through the biosphere;
for example, the sulphur cycle.
aspect
The compass orientation of sloping ground or
any other landscape feature. May be measured as an
azimuth angle from North.
biosphere
The totality of all living things.
asthenosphere
The relatively weak and ductile sphere
of rock lying beneath the lithosphere and occupying the
uppermost part of the mantle that allows continents to
move. Also called the rheosphere.
biota
All the animals and plants living in an area.
bluffs
The steep slopes that often mark the edge of
a floodplain.
atmosphere
The dusty, gaseous envelope of the Earth,
retained by the Earth's gravitational field.
breccia
A bedded, rudaceous rock consisting of angular
fragments of other rocks larger than 2 mm in diameter
cemented in a fine matrix.
atoll
A circular or closed-loop coral reef that encloses
a lagoon.
calcareous
Any soil, sediment, or rock rich in calcium
carbonate.
bacteria
Micro-organisms, usually single-celled, that
exist as free-living decomposers or parasites.
calcite
A crystalline form of calcium carbonate
(CaCO
3
). The chief ingredient of limestone, marble, and
chalk. A natural cement in many sandstones.
backswamp
An area of low-lying, swampy ground
lying between a natural levee and the valley sides on the
floodplain of an alluvial river.
cation
A positively charged ion.
badlands
A rugged terrain of steep slopes that looks
like miniature mountains. Formed in weak clay rocks or
clay-rich regolith by rapid fluvial erosion.
cavitation
A highly corrosive process in which water
velocities over a solid surface are so high that the
vapour
pressure
of
water
is
exceeded
and
bubbles
form.
barrier reef
A coral reef that is separated from the
mainland shoreline by a lagoon.
chalk
A soft, white, pure, fine-grained limestone.
Made of very fine calcite grains with the remains of
microscopic calcareous fossils.
basalt
A hard, but easily weathered, fine-grained, dark-
grey igneous rock. The commonest rock produced by a
volcano, it consists mainly of calcic-plagioclase feldspar,
chamosite
A hydrous iron silicate.
