Geology Reference
In-Depth Information
dolomite
A mineral that is the double carbonate
of calcium and magnesium, having the chemical for-
mula (CaMg)CO
3
. The chief component of dolomitic
limestones.
flood
A short-lived but large discharge of water cours-
ing down, and sometimes overflowing, a watercourse.
flood basalts
Basalt erupted over a large area.
fulvic acid
An organic acid formed from humus.
eclogite
A
coarse-to-medium-grained
igneous
rock
made mainly of garnet and sodic pyroxene.
gabbro
A group of dark-coloured plutonic rocks,
roughly the intrusive equivalent of basalt, composed
chiefly of pyroxene and plagioclase, with or without
olivine and orthopyroxene.
ecosphere
The global ecosystem - all life plus its life
support system (air, water, and soil).
endogenic
Of, or pertaining to, the Earth's interior
(cf. exogenic).
gastropod
Any mollusc of the class Gastropoda.
Typically has a distinct head with eyes and tentacles, and,
in most cases, a calcareous shell closed at the apex.
episodic
Events that have a tendency to occur at
discrete times.
gibbsite
A form of alumina and a component of
erosion
The weathering (decomposition and disinte-
gration), solution, corrosion, corrasion, and transport of
rock and rock debris.
bauxite.
gley
A grey, clayey soil, sometimes mottled, formed
where soil drainage is restricted.
erosion surface
A more or less flat plain created by
erosion; a planation surface.
gneiss
A coarse-grained, banded, crystalline metamor-
phic rock with a similar mineralogical composition to
granite (feldspars, micas, and quartz).
eustatic
Referring to a true change of sea level, in con-
trast to a local change caused by the upward or downward
movement of the land.
goethite
A brown-coloured, hydrated oxide of iron;
the main ingredient of rust.
exogenic
Of, or pertaining to, the surface (or near the
surface) of the Earth (cf. endogenic).
gorge
A steep-sided, narrow-floored valley cut into
bedrock.
exsudation
A type of salt weathering by which rock
surfaces are scaled off, owing to the growth of salt and
gypsum crystals from water raised by capillary action.
granite
A coarse-grained, usually pale-coloured, acid,
plutonic rock made of quartz, feldspar, and mica. The
quartz constitutes 10-50 per cent of felsic compounds,
and the ratio of alkali feldspar to total feldspar lies in
the range of 65-90 per cent. Biotite and muscovite are
accessories. The feldspar crystals are sometimes large,
making the rock particularly attractive as a monumental
stone. In the stone trade, many hard and durable rocks
are called granite, though many of them are not granites
according to geological definitions of the word.
feldspar
A group of minerals including orthoclase and
microline, both of which are potassium alumino-silicates
(KAlSi
3
O
8
), and the plagioclase feldspars (such as albite
and anorthite). Albite contains more than 90 per cent
sodium alumino-silicate (NaAlSi
3
O
8
); anorthite con-
tains more than 90 per cent calcium alumino-silicate
(CaAlSi
3
O
8
). Calcic feldspars are rich in anorthite.
Alkali feldspars are rich in potash and soda feldspars,
contain relatively large amounts of silica, and are charac-
teristic minerals in acid igneous rocks.
granodiorite
A class of coarse-grained plutonic rocks
made of quartz, plagioclase, and potassium feldspars with
biotite, hornblende or, more rarely, pyroxene.
flag (flagstone)
A hard, fine-grained sandstone, usu-
ally
containing
mica,
especially
along
the
bedding
gravel
A loose, unconsolidated accumulation of
rounded rock fragments, often pebbles or cobbles. Most
gravels also contain sand and fines (silt and clay).
planes.
Occurs
in
extensive
thin
beds
with
shale
partings.
