Geology Reference
In-Depth Information
greywacke
A
dark-grey,
firmly
indurated,
coarse-
hydrothermal
Associated with hot water.
grained sandstone.
hydrous minerals
Minerals containing water, espe-
cially water of crystallization or hydration.
grit (gritstone)
A name used, often loosely, to describe
a coarse sandstone, especially one with angular quartz
grains that is rough to the touch.
hydroxyl
A radical (a compound that acts as a single
atom when combining with other elements to form
minerals)
made
of
oxygen
and
hydrogen
with
the
groundwater (phreatic water)
Water lying within the
saturation zone of rock and soil. Moves under the
influence of gravity.
formula (OH).
hypabyssal
Said of rocks that solidify mainly as minor
intrusions (e.g. dykes or sills) before reaching the Earth's
surface.
grus
A saprolite on granite consisting of quartz in a clay
matrix.
Ice Age
An old term for the full Quaternary glacial-
interglacial sequence.
gypsum
A
white
or
colourless
mineral.
Hydrated
calcium sulphate, CaSO
4
.2H
2
O.
ice age
A time when ice forms broad sheets in mid-
dle and high latitudes, often in conjunction with the
widespread occurrence of sea ice and permafrost, and
mountain glaciers form at all latitudes.
halite (rock salt, common salt)
Sodium
chloride,
NaCl,
although
calcium
chloride
and
magnesium
chloride
are
usually
present,
and
sometimes
also
magnesium sulphate.
illite
Any of three-layered, mica-like clay minerals.
halloysite
A clay mineral, similar to kaolinite, formed
where aluminium and silicon are present in roughly
equal amounts, providing the hydronium concentra-
tion is high enough and the concentration of bases
is low.
infiltration
The penetration of a fluid (such as water)
into a solid substance (such as rock and soil) through
pores and cracks.
inselberg
A large residual hill within an eroded plain;
an 'island mountain'.
hematite
A blackish-red to brick-red or even steely-
grey oxide of iron (Fe
2
O
3
), occurring as earthy masses or
in various crystalline forms. The commonest and most
important iron ore.
intermittent stream
A stream that, in the main,
flows though a wet season but not through a dry
season.
hillslope
A slope normally produced by weathering,
erosion, and deposition.
ion
An atom or group of atoms that is electrically
charged owing to the gain or loss of electrons.
hornblende
A mineral of the amphibole group.
ionic load
The cargo of ions carried by a river.
humic acid
An organic acid formed from humus.
island arc
A curved line of volcanic islands linked to
a subduction zone.
hydraulic conductivity
The flow rate of water
through soil or rock under a unit hydraulic gradient.
Commonly measured as metres per day.
isostasy
The idea of balance on the Earth's crust, in
which lighter, rigid blocks of crustal material 'float' on
the denser, more plastic material of the mantle. The
redistribution of mass at the Earth's surface by ero-
sion and deposition or by the growth and decay of ice
upsets the balance causing the crustal blocks to float
higher or lower in the mantle until a new balance is
achieved.
hydrosphere
All the waters of the Earth.
hydrostatic pressure
The pressure exerted by the
water at a given point in a body of water at rest. In gen-
eral, the weight of water at higher elevations within the
saturated zone.
