Geology Reference
In-Depth Information
jökulhlaup
A glacier burst - the sudden release of
vast volumes of water melted by volcanic activity under
a glacier and held in place by the weight of ice until the
glacier eventually floats.
marble
Limestones that have been crystallized by
heat or pressure, though some special types of
non-metamorphosed limestones are called marble. Pure
marble is white.
juvenile water
Primary or new water that is known not
to have entered the water cycle before. It may be derived
directly from magma, from volcanoes, or from cosmic
sources (e.g. comets).
marcasite
White iron pyrites, an iron sulphide with
the identical composition to pyrite (
see
pyrite).
marl
A soft, mainly unconsolidated rock made of
clay or silt and fine-grained aragonite or calcite mud.
The clay or silt fraction must lie in the range 30-70
per
kaolinite
A 1 : 1 clay mineral, essentially a hydrated
aluminium silicate formed under conditions of high
hydronium (hydrated hydrogen ion, H
3
O
+
) concentra-
tion and an absence of bases. Its ideal structural formula
is Al
2
Si
2
O
5
(OH)
4
.
knickpoint
An interruption or break of slope, espe-
cially a break of slope in the long profile of a river.
cent.
Marls
are
friable
when
dry
and
plastic
when wet.
marlstone
Consolidated marl.
mesosphere
A transition zone between the astheno-
sphere and the lower mantle.
metamorphism
The processes by which rocks are
transformed by recrystallization owing to increased heat
or intense pressure or both.
landslide
A general term for the
en masse
movement
of material down slopes.
laterite
A red, iron-rich, residual material with a rich
variety of definitions.
meteoric water
Water that is derived from precip-
itation and cycled through the atmosphere and the
hydrosphere.
lava
Molten rock.
mica
A group of minerals, all hydrous alumino-silicates
of potassium, most members of which may be cleaved
into exceptionally thin, flexible, elastic sheets. Muscovite
(or white mica) and biotite (or dark mica) are common
in granites.
leaching
The washing-out of water-soluble materials
from a soil body, usually the entire solum (the genetic soil
created by the soil-forming processes), by the downwards
or lateral movement of water.
limestone
A
bedded
sedimentary
rock
composed
mineral
A naturally occurring inorganic substance,
normally with a definite chemical composition and
typical atomic structure.
largely of the mineral calcite.
limonite
A hydrated iron oxide, FeO(OH).
n
H
2
O;
not a true mineral as it consists of several similar hydrated
iron oxide minerals, and especially goethite.
monadnock
An isolated mountain or large hill rising
prominently from a surrounding peneplain and formed
of a more resistant rock than the plain itself.
lithified
The state of being changed to rock, as when
loose sediments are consolidated or indurated to form
rocks.
mud
A moist or wet loose mixture of silt- and clay-
sized particles. Clay is a mud in which clay-sized particles
predominate, and silt is a mud in which silt-sized
particles predominate.
lithology
The physical character of a rock.
magma
Liquid rock coming from the mantle and
occurring in the Earth's crust. Once solidified, magma
produces igneous rocks.
mudstone
A sedimentary rock, consisting mainly of
clay-sized and silt-sized particles, with a massive or blocky
structure and derived from mud. If clay-sized particles are
dominant, the rock is a claystone; if silt-sized particles
magnesian limestone
A
limestone
containing
an
appreciable amount of magnesium.
