by Dr J Floor Anthoni
What stands between you and the knowledge
of the Earth is not as much the understanding of it, but the many new words
necessary for describing the many geologic features and processes. This
glossary aims to help you to translate and to remember these new words.
Use it as a reference or print it out. Just reading it, is interesting.
A.B.C.D.E.F.G.H.I.J.K.L.M.N.O.P.Q.R.S.T.U.V.W.X.Y.Z A --
Ablation: (L: ab=away, from; lat= past part stem
of ferre=to carry) all processes by which snow and ice are lost
from a glacier.
Abrasion: (L: ab=away; radere=to scrape)the mechanical
wearing or grinding away of rock surfaces by the friction and impact of
Acidic: (L: acidus= sour; acidere= to be sour)
rock containing more than 60% silica. Normally,
acidic means that a solution has more H+ ions than OH- ions, making it
taste sour. But in the rocks from a magma
melt, the term is used to grade rock by its silica concentration. Rock
with little silica (less than 40%) is called basic.
Acidification: the various processes that make a soil more sour
and less suitable for most plants. Naturally, carbon dioxide binds with
water to form a mild acid. Leaf litter with a high content of resins, is
decomposed producing acids. Sulphuric acid is part of natural rainwater
but is also found in much higher concentrations in acid rain from industries.
Nitric acid is also formed from industrial smoke. Nitrogen fertilisers
like ammonium nitrate can break down to nitric acid in the soil.
Accretion: (L: ad=to/onto; crescere= to grow)
the growing of separate things into one. The gradual addition of new land
to old by sedimentation or plate tectonics.
Accumulation: (L: ad=to/onto; cumulus=heap) growing
by heaping up. See also accretion.
Adobe: (Spanish) a mixture of clay and silt, found in the desert
basins of the USA and Mexico, extensively used for building in the form
of sun-dried bricks.
Aeolian: (L: Aeolus= god of the winds) transported by
Agate: a translucent cryptocrystalline
variety of quartz, being a variegated chalcedony
or alternating with opal.
Aggrade: (L: ad=to/onto; gradus=step) opposite
of degrade. The process of building up a surface
Albite: (L: albus=white) a feldspar,
usually white, rich in sodium. NaAlSi3O8. A variety of plagioclase common
in igneous and metamorphic rock
Alfisols: (?) soils with clay-enriched subsoils. See rocktable/soil.
Allitic weathering: forming 1:1 clays or two-layer clays. Typical
of humid, warm areas; formed through rapid leaching of silica.
Alluvium: (L: ad= to/onto; luere=wash) sediment
deposited by rivers and streams. It ranges from clays, through silts and
sands to gravels.
Alum: a colourless or white mineral with a sweet-sour astringent
taste. KAl(SO4)2.12H2O. Used to stem blood flow from wounds after shaving.
Alumina: oxides of aluminium. Al2O3.
Amorphous clays: (L/Gk: amorphus/ amorphos= shapeless,
formless) clays consisting of a mix of iron and aluminium sesquioxides
(Fe2O3, Al2O3), lacking the layered structure of one- and two-layer clays.
Amphibole: (L/Gk: amphibolia= ambiguous) the horneblende
minerals that are confusing because of their many forms.
Andesite: (Andes= mountain chain in S. America) a fine-grained
brown or greyish intermediate extrusive volcanic
Andisol/ andosol: (Andes= mountain chain in S.America) soil
originating from volcanic ash.
Ando: (Andes= mountain chain in S America) volcanic ash.
Anion: a negatively charged ion such as OH-, SO4--.
Anorthite: plagioclase calcium
White to medium gray with striations (stripes). CaAl2Si2O8.
Apatite: (Gk: apate= deceit, from its deceptive forms)
a naturally occurring crystalline mineral of calcium phosphate and fluoride,
used in the manufacture of fertilisers. Ca5(PO4,CO3)3(F,OH,Cl).
Argillic development: (Gk: argos= white) the development
of a hard layer of silicate clays in the soil, restricting soil depth root
Argillite: (Gk: argos=white) a sedimentary rock composed
of clay particles which have been hardened and cemented. Argil = pottery
clay. Marl and shale smell earthy when breathed upon.
Aridisols: (L: aridus= dry; solum= ground) soils
of deserts and semi-arid regions, and related saline or alkaline soils.
Asbestos: (Gk: asbestos= unquenchable; a-=not;
sbennumi=quench) a hydrated silicate mineral of the serpentine
(chrysotile asbestos) or amphibole group.
Hydrated silicates are minerals composed of silica
and a metallic element, which are chemically combined with water. Chrysotile,
the best known, most abundant, and widely used type of asbestos, consists
of alternate sheets of magnesia and silica,
coiled into extremely fine tubes called fibrils. Amphibole asbestos has
coarser fibres than chrysotile.
Ash: see tephra.
Asthenosphere: (Gk: asthenes=weak) a hot, soft layer
of the earth's mantle, on which the lithosphere
Augite: (Gk: auge= lustre) a complex calcium magnesium
aluminous silicate occurring in many igneous rocks. One of the most common
Autochthonous soils: (Gk: auto= self; chthonos=
earth) original soils found at the place where they were formed by weathering.
Bank collapse: mass movement of stream banks, once under-cut
by the scouring action of floodwater.
Basalt: (Gk: basanos= touchstone) a dark basic
extrusive volcanic rock whose strata sometimes form columns. It
consists mainly of the minerals plagioclase feldspar
and pyroxene. Rich in iron and magnesium-bearing
minerals, poor in silica and characteristic
of the ocean's crust.
Basic: (L: basis= stepping; bassus= short) rock
having less than 50% silica. Normally, basic means a liquid with more OH-
ions than H+ ions.
Biotite: (Named after the French physicist J B Biot who
died in 1862) a black, dark brown or green micaceous (mica-like)
mineral occurring as a constituent of metamorphic
and igneous rocks.
Blanking: replacement of any seedling trees that have died and
left blanks in a regular planting pattern.
Braided channel: a river channel that has numerous branches,
separated by exposed alluvial bars.
Breccia: a volcanic rock, composed
of angular mineral fragments embedded in a matrix, the product of explosive
Calcification/ calcify: (L: calx= lime) to become
hardened by the depositon of calcium salts.
Caldera: (L: caldus/calidus=warm; caldarius= steam
room; Spanish: caldaria= boiling pot) A large volcanic depresssion,
often a large crater with other craters or volcanoes inside.
Carbon ignition: conversion of soil organic matter to CO gas,
by high temperture reaction, when overlying vegetation is burned.
Catalist: (Gk: kata=down; luo=set free) substances
that speed up a chemical reaction without being consumed by the reaction.
Cation: a positively charged ion such as H+, Mg++, Ca++, K+.
Cation Exchange Capacity: the capacity of soil minerals,
particularly clays, to attract, retain and exchange positively charge ions
(cations). It is measured in units of centimole/kg of dry soil.
CEC: see cation exchange capacity.
Check dam: steel and concrete structure in a mountain torrent,
designed to trap sediment and to prevent scour by debris
Chernozem: (Russian: chernyi= black; zemlya=earth)
also called black earth, is a fertile black soil rich in humus,
found in temperate regions, particularly in southern Russia. High in silicate
clay minerals with minimal clay illuviation and a dark coloured A horizon
containing at least 4% organic matter.
Chondrite, carbonaceous: (Gk: chondros=granule)
a type of stony meteorite containing small mineral nodules, rich in water
and light elements such as carbon. Assumed to resemble the original material
of the mantle.
Clastic: (Gk: klastos= broken in pieces) composed of
broken pieces of older rocks. Clastic rocks are conglomerates, sandstone,
Close planting: plantation of trees sufficiently dense to form
a continuous or close canopy. Seedling trees planted at densities of 1000
stems a hectare or more, form a close canopy within 5 to 10 years, depending
on species. Mature trees maintain a close canopy even if thinned to 200-400
stems per hectare.
Collapse hole: circular hole in topsoil, caused by its collapse
into a tunnel (under-runner) in the subsoil.
Colloid: (Gk: kolla=glue) ultra small solid particles
dispersed in liquid, not settling out. See also emulsion. Whereas emulsions
are liquid 'particles' dispersed into another liquid, into which it won't
dissolve, colloids are solid particles dispersed into a liquid.
Colluvium: (L: collis= hill; luere= to wash; hill-washed)
gravity-transported soils. Slips and earth slumps can transport soil.
Condition (law): a formal restriction on the way land is used,
attached to a resource consent, issued by a district or regional council,
or written as a rule in a district or regional plan.
Coquina: (Spanish: coquina= cockle) a soft limestone
of broken shells, often used for road-making.
Corundum: (Tamil: kurundam; Sanskrit kuruvinda=ruby)
an extremely hard crystalline alumina (aluminium oxide) used especially
as an abrasive, and varieties of which (ruby, sapphire) are used for gemstones.
Craton: (?) a stable portion of a continent, commonly of Precambrian
age, and not deformed for a long time.
Crust: (L: crusta= rind, shell) the upper solid shell
of the earth, separated from the underlying mantle by the Mohorovicic discontinuity,
and of lower density than the mantle.
Cryptocrystalline: (Gk: cryptos= hidden) texture of a
rock with crystals that are to small to be recognised under a microscope.
Crystal: a clear, transparent mineral.
Dacite: (?) An extrusive igneous rock in composition between
(thick) and andesite (fluid), consisting mainly
of the minerals feldspar and quartz.
Dacite flows less easily than andesite, and releases its dissolved gases
with explosions, forming pumice in the process. Rhyolite is even more explosive.
Debris dam: (Fr: débriser= to break down) timber
and netting structure in a hillside gully, designed to trap sediment and
to prevent scour by runoff.
Degrade: (L: de,dis=negation, not; gradus=step)
to reduce to a lower form.
Density (vegetation): the thickness of plant cover growing on
a given area of land, usually expressed as a percentage of cover
for grass, or as stems per hectare for trees.
Desilicification: the loss of silica and siliceous compounds.
Diatomite: (Gk; dia=two; temmo=to cut; diatomos=
two-halved, referring to the pill-box shape of diatoms) a silica deposit
originating from the siliceous frustules (shells) of marine and freshwater
diatoms. Because of its high surface area, absorptive capacity and chemical
stability, it is used as a mild abrasive, in filtration, insulation and
Diorite: (Gk: diorizo= to distinguish) a coarse-grained
igneous rock containing quartz. Consists
mainly of feldspar, amphibole and biotite.
Dodecahedron: (Gk: dodeka= twelve; hedron= seat)
a solid figure with twelve faces.
Dolomite. (French geologist: D de Dolomieu, died in 1801)
a mineral of calcium magnesium carbonate.
Downs: undulating, low hills, usually with slopes gentle enough
to be cultivated.
Dystrophic: (Gk: dys= bad; trepho= to feed, nourish)
lacking nutrients. Nutrient-deficient. Opposite of eutrophic
Effervescence: (L: ex=out of; fervere= to be hot)
foaming of soil or rock in reaction to hydrochloric acid (HCl); the 'acid
test'. Particularly because of its carbonate (CaCO3, MgCO3) content. In
arid climates, effervescence is found in the B horizon.
Eluviate: (L: ex= out of; luere= to wash) to leach
outward. The loss of nutrients and minerals upward and out of the soil
Emulsion: (L: ex=out/from; mulgere= to milk) a
fine dispersion of one liquid in another but not dissolving, often looking
Entisol: (?) soils without layering, except after ploughing.
Environmental effect: any impact which a land use has on soil,
water, air, plants or animals.
Enrichment: planting timber trees (either exotic or indigenous)
in regenerating scrub.
Enstatite: a mineral of MgSiO3 with colours ranging from white
through brown to grey.
Ephemeral (stream): (Gk: epi=upon hemeros=lasting
one day; hemera=day) a water course which flows after heavy rain,
and dries up during fine weather.
Epidote: a calcium/aluminium/iron silicate Ca2(Al,Fe)3[OH/(SiO4)]3
Erosion: (L: ex=out of; rodere= to gnaw) the stripping
of soil and weathered rock from landforms; creating sediment for transport
by water, wind or ice, and enabling the formation of new sedimentary deposits.
Eutrophic: (Gk: eu= well; trepho= to feed/ nourish)
rich in nutrients.
Evaporite: (L: ex=out of; vaporare= steaming;
a sedimentary rock produced by the evaporation of seawater and precipitation
of its salts. It contains a wide range of components, among which rock
salt and gypsum.
Extrusion/extrusive: (L: ex= out of; trudere=
to thrust) molten volcanic rock deposited
on the surface and cooled rapidly.
Facies: (L: facies=face) the character of rock etc, expressed
by its composition, fossil content etc, reflecting the environment in which
it was formed.
Farm improvements: buildings, yards, fences, tracks, drains,
ponds, water reticulation.
Fault: a fracture in a rock body along which one side has been
displaced, relative to the other.
Fayalite: Fe2SiO4. An olivine silicate,
dark-green or black.
Feldspar: (German: felspat) any of a group of aluminium silicates
of potassium, sodium, or calcium, which are the most abundant minerals
in the earth's crust.
Ferrugination: (L: ferro= iron; ferruginis= rust)
iron sesquioxides adhere firmly to sand and gravel, giving them a red colour,
and may cement them to form a subsurface iron pan.
Floodplain: low-lying alluvium
immediately adjacent to a river or stream, inundated as soon as it overflows
Fluorite: (L: fluere= to flow; fluor= melting
flux) a mineral form of calcium fluoride (fluorspar).
Formation: (L: forma= form) a suite of rocks with common
characteristics distinguishing it from other suites nearby and traceable
or mappable over a reasonably large area. An assemblage of strata having
some common characteristic.
Fracture zone: a dislocation at right angles to a mid-ocean
ridge, usually marked by a set of transverse ridges and troughs.
Fragipan: (?) A soil horizon consisting of an irregular, very
hard accumulation of acid clay, thought to have formed by clay seeping
down cracks in the profile.
Gabbro: (It: Gabbro in Tuscany) a dark, granular plutonic
rock of crystalline structure.
Gabion: (It: gabbia= basket) a wire basket filled with
rocks, used to stabilise a riverbank or foot of an unstable slope. Also
used in fortification.
Garnet: (L: granatum= pomegranate, from its resemblance
to the pulp of the fruit) a vitreous (glassy) silicate mineral, especially
a transparent deep-red kind used as a gem.
Geology: (Gk: ge=earth; logike= art of reason)
the science of the earth, including the composition, structure, and
origin of its rocks.
Geography: (Gk: ge=earth; graphe=writing) the
study of the earth's physical features, resources and climate, and the
physical aspects of its population.
Geosyncline: (Gk: ge=earth; syn= with; klino=to
slope) a large, elongated depression in earth's crust in which thick sediments
accumulate, followed by deformation into a mountain range.
Gibbsite: Aluminium hydroxide. Al(OH)3. Found in aluminium ore.
The most common hydrated aluminium oxide found in soils, consisting of
a double layer of hydroxyl molecules enclosing aluminium in the octahedral
Glacial: (L: glacies=ice) characterised or produced in
the presence of ice. Glacial epoch = an interval of cold climate leading
to great expansion of continental icecaps.
Gleisation: (gley = Ukrainian word for clay) under waterlogging
conditions, iron becomes ferrous (Fe++). Ferrous soils consist of sticky
clay with a grey-blue colour, and are called gley. Because ferrous iron
is more mobile than ferric iron (Fe+++), it may get eluviated from the
soil, resulting in a leached upper horizon.
Gneiss: (German: Gneiss) a coarse-grained metamorphic
rock foliated by mineral layers, principally of feldspar,
and ferromagnesian minerals.
Granite: (L: granon= grain) a granular crystalline igneous
rock of quartz, mica, feldspar, etc., used
Granodiorite: an intrusive crystalline igneous
rock with properties in between granite and
Greenstone belt: an elongated, folded complex of slightly altered
sediments and volcanic rocks of oceanic and
intermediate character, usually of Precambrian age.
Greenstone: 1) a greenish igneous
rock containing feldspar and hornblende.
2) a variety of jade found in New Zealand.
Greywacke: a sedimentary rock composed of silt or sand particles
which have been hardened and cemented.
Groundwater: water which flows through pores and fissures in
soil or rock, beneath the water table.
Gullying: erosion of soil or rock by ephemeral
streams, downcutting through hill slopes after heavy rain.
Gypsum: (Gk: gypsos= gypsum) a hydrated form of calcium
sulphate, occurring naturally and used in the building industry and to
make plaster of Paris.
Halite: (Gk: hali/hals= sea; hals= salt) rock-salt,
not obtained by evaporating seawater.
Heavy soil: soil with a high ratio of clay to sand or silt;
sticky when wet, hard when dry, and difficult to cultivate.
Hill country: steep land with slopes greater than 20 degrees,
but low relief, typically to 100-300 m difference in elevation. Valley
bottoms are usually narrow.
High country: mountainous land with steep slopes and a high
relief; typically more than 300 m difference in elevation. Slopes are usually
separated by broad, flat valley bottoms, infilled by alluvium.
Histosols: (Gk: histos=web; solum=ground) ?
Horizon: functionally different layers within the soil profile.
O, A, B, C, R horizons.
Hornblende/ horneblende: (German) a dark-brown, black or green
occurring in many igneous and metamorphic
rocks, and composed of calcium, magnesium and iron silicates.
Hotspot: an anomalously hot area in the mantle below the lithosphere,
source of volcanic activity in a plate as
it passes overhead.
Humification: (L: humus= soil) the process of forming
humus from organic matter. Soil organic mater can be doubled in 5-50 years.
Humus: (L: humus= soil) residues from organic matter
like leaves, roots, algae and soil organisms, transferred by microorganisms
into a mixture with soil minerals. Humus is a persistent form of organic
matter that is not easily broken down.
Hydrargillite: (Gk hydor= water; argos= clay)
aluminium hydroxide (Al(OH)3), a colourless white sediment.
Hydrothermal: (Gk: hydor=water; therme=heat) the
activity of hot waters in the crust.
Hygroscopic: (Gk: hygros=moist,wet; skopeo=to look at)
the ability to take in water from the atmosphere.
Hypersthene: (Gk hyper= over/beyond; sthenos=
strength, being harder than hornblende) a
rock forming greenish mineral of magnesium
iron silicate, harder than hornblende.
Igneous: (Lat: ignis = fire) arising from hot liquid
magma deep inside the earth. Volcanic.
Ignimbrite: sheets of coalesced fine particles which once
flowed at high speed as extremely hot fluid (pyroclastic
flow) avalanches down a volcano. The high heat of over 1000ºC
coalesces all particles to form rock, looking like concrete (welded ignimbrite).
Illuvial horizon: a horizon formed by the deposition of materials
leached out of an overlaying layer.
Illuviate: (L: in=in/into; luere= to wash) similar
to leaching. Loss of minerals and nutrients by water, moving down in the
Inceptisols: (?) very young soils with weakly developed
soil layers, and not much leaching or mineral alteration.
Intermediate: (L: inter= between, among; medius=
middle) rock consisting of about 50% silica.
Intrusion/ intrusive: (L: intrudere; intrus= into;
to thrust) an influx of molten rock between or through strata, but not
reaching the surface; cooling slowly.
Isostasy: (Gk: isos=equal; stasis= station) the
general state of equilibrium with the rise and fall of the earth's crust
as a result in changes in its buoyancy.
Jade: (Spanish: piedra de ijeda= stone of the flank,
thought to cure colic, a severe spasmodic abdominal pain) a collective
term for jadeite NaAlSi2O6 and nephrite Ca2(Mg,Fe)5(OH,F)2Si8O22.
Kaolin/kaolinite: (Chinese: gaoling; gao=high;
hill) a fine soft white clay produced by the decomposition of other clays
of feldspar, used especially for making porcelain, and in medicines. Also
called china clay.
Kaolisol: (from kaolin and soil) soils of the
humid tropics that contain more bases in their upper horizon, than below,
which is opposite to the norm.
Karst: (= a limestone region in YugoSlavia) a limestone region
with underground drainage and many passages and cavities caused by the
dissolution of the rock.
Krasnozem: (?) a deep, red soil formed under free drainage in
the humid tropics. Its clayey texture is dominated by sesquioxides.
Kyanite: (Gk: kyanos= dark blue) a blue crystalline mineral
of aluminium silicate.
Lahar: (Javanese) a mud flow formed through interaction of pyroclastic
flows with water from melting ice, crater lakes or rain. Having high
density (weight), mud flows are fast, and they scour the river beds through
which they flow, accumulating more mass as they go, and causing serious
damage and hazard to life.
Laterite/ic: (L: later= brick) Laterite is a red or yellow
ferruginous clay, friable and hardening in air, used for making roads in
the tropics. Lateritic soil is sesquioxide-dominated, deeply weatherd,
containing sequences of horizons of laterite.
Lava: (L: lavare= to wash) molten volcanic
rock and the rock formed after cooling.
Leaching: (Old-English: leccan= to water; Dutch: lekken=
to leak) the loss of water-soluble minerals and nutrients from the soil
Light soil: soil with a high ratio of sand or silt to clay;
aggregated when wet, but powdery and difficult to cultivate when dry.
Lithosphere: (Gk lithos= stone) the hard and solid, outermost
layer of the Earth.
Lithosol: (Gk: lithos= stone) stony soil with shallow
profiles as found on steep mountains.
Loam: (Old-English Lam) a soil with substantial proportions
of clay, silt and sand, with an aggregated structure enabling easy cultivation,
whether wet or dry.
Loess: (German: loesen= to loosen) silt deposited by
winds blowing across sparsely vegetated ground during the last ice age.
It mantles many plains, terraces and downs in areas near ancient glaciers.
Very fertile when irrigated.
Magma: (Gk: magma/ masso= to knead) fluid or semifluid
material deep inside the earth from which igneous rock is formed.
Magnetite: (Magnesia= an island in Asia Minor, from which
magnetic rock was obtained) black, unhydrated magnetic iron oxide.
Marble: (L: marmor; Gk: marmaros= shining stone)
limestone in a metamorphic crystalline (or
granular) state, and capable of taking a polish. Used in sculpture and
Mass movement: erosion of soil or rock by gravity-induced collapse.
Usually triggered by groundwater pressure after heavy rain, but can also
have other causes, notably streams undercutting the base of a slope, or
earthquakes. Movement can either be rapid and near-instantaneous (landslides,
avalanches, debris flows) or slow and intermittent (earthflows, slumps).
Metamorphic/ metamorphism: (Gk: meta= with/after;
form) rock that has undergone transformation by natural agencies such as
heat and pressure.
Mica: (L: mica=crumb) any of a group of silicate minerals
with a layered structure, especially muscovite.
Mica-schist: a fissile rock containing quartz and mica.
Mineral: (L: minera=ore) a solid, inorganic substance,
found in nature, which has an orderly internal structure and a specific
Mohorovicic discontinuity (Moho): (named after Mohorovic)
the boundary between crust and mantle, marked by a sharp decrease in earthquake
Mollisols: (L: mollis=soft; solum=ground) grassland
soils, mostly rich in calcium; also forest soils developed on calcium-rich
parent materials. They are characterised by a thick surface layer, rich
in organic material.
Montmorillonite: (Montmorillon= a place in the south
of France) a three-layer clay (smectite group), capable of high cation
exchange and holding large amounts of water. Sticky when wet.
Mudstone: a sedimentary rock composed of silt and clay particles,
compacted and weakly cemented together by a small quantity of lime.
Muscovite: (L: Muscovia= moscow) a silver-grey form of
with a sheetlike crystalline structure that is used in the manufacture
of electrical equipment, etc.
Nitrogen volatilisation: (volatile= evaporative. L: volare=
to fly) conversion of soil nitrogenous matter to NO and NO2 gas, by high-temperature
reaction when overlying vegetation is burned, or by bacteria in the soil.
Nontronite: (?) an amorphous smectite clay formed from weathered
volcanic ashes, basalt. Na(0.33)Fe2(Al(0.33)Si(3.67))O10(OH)2.nH2O.
Octahedron: (Gk: okto=eight; hedra= seat) a body
(crystal) contained within eight triangular planes of equilateral triangles.
Olivine: (Say: "olivene") (olive-green colour) a naturally
occurring form of magnesium-iron silicate, usually olive-green and found
in igneous rocks. Other names: peridot, chrysolite.
Organic load: the quantity of organic matter passing a stream
reach in the course of a year. Usually expressed in terms of biological
oxygen demand, i.e the amount of oxygen consumed by micro-organisms as
they break it down.
Orogeny: (Gk: oros=mountain; genes=born, of a
specified kind; gignomai=be born, become) mountain building, involving
deformation, metamorphism, uplift and intrusion
of igneous rock. It happens when continents collide.
Orthoclase: (Gk ortho=straight; klasis=cleavage)
a common alkali feldspar usually occurring
as variously coloured crystals, used in ceramics and glassmaking.
Orthorhombic: (Gk: orthos= straight; rhombos=
a parallelogram with oblique angles and equal sides, a rhombus ) a crystal,
characterised by three mutually perpendicular axes, which are unequal in
length, such as in topaz and talc.
Outwash: alluvial sand and gravel
deposited by rivers, draining glaciers during the last ice age. Widespread
on terraces and floodplains in areas near ancient glaciers.
Oxysols: (Gk oxus=sharp) Soils that are more weathered
than the ultisols, including most laterites.
Pair planting: plantation of trees in pairs on either side of
a hill slope watercourse, to prevent gully incision.
Parent material: the bedrock underneath the soil, from which
the soil originated.
Ped: (Gk: pedon=ground) a crumb of soil.
Pedalfer: () soil of humid climate.
Pedocal: () soil of arid climate.
Pedology: (Russian: pedologiya: soil study; Gk: pedon=
ground) the scientific study of soils, especially its formation, nature
Peridotite: (Old-French: peritot) A heavy intrusive
igneous rock mainly consisting of olivine
and 5-15% pyroxene. Peridot: A green
variety of olivine, used especially as a precious
Perlite: (French: perle=pearl) a vermiculite
volcanic glass with the composition of rhyolite.
When heated, it pops, to form a light-weight aggregate for construction.
Permafrost: (from permanent + frost) subsoil which remains
below freezing point throughout the year, as in the polar regions.
Phreatic: (Gk: phreatos= well) driven by (ground) water.
Phreatic eruptions throw out old, previously cooled rock as a result of
sudden violent interaction between hot rock or gas and groundwater. This
kind of eruption is also called pyroclastic surge or base surge,
resulting in base surge deposits.
Plagioclase: (Gk: plageos= oblique; klasis=cleavage)
a series of feldspar minerals forming glassy
Planosol (or solod): (L: planus= flat; solum=
ground) calcium- or hydrogen-saturated soils with considerable difference
in clay content between the eluviated surface
(top) and the clay illuvial horizon (below).
Plutonic: (L/Gk: Plouton= god of the underworld) formed
as igneous rock by solidification below the
surface of the earth.
Podsol/isation: also podzol/isation (Russian: pod=under;
ashes) weathering in a strongly acid medium eluviatesthe
iron and aluminium oxides, causing the formation of amorphous
clays with high CEC. The soil gets
an upper horizon rich in sand and an illuvial
horizon rich in amorphous clays (spodic
These soils are called podsols. Best developed under pine forests.
Precipitate: (L: prae=before; caput=head; praecipitare=
to head before) causing to be deposited onto a surface; moisture condensed
Profile: (L: pro= for, on behalf of, infavour of; filare=to
spin; filum= thread) an outline, a cross-section. A soil profile
is a cross- section through the soil.
Pumice: (L: pumex/ pumicis= pumice stone) a light-weight
and light-coloured, cellular glassy rock with the composition of rhyolite.
Pumice forms when lava from a volcano flows onto the earth's surface or
erupts violently into the air. The hot, gas-filled lava then cools
quickly to form glass. Many tiny holes remain after the volcanic
gases escape from the cooling lava. Pumice floats on water because
it contains many air bubbles. Used as light-weight aggregate and for scouring.
Also see tephra.
Pyrite (Fool's Gold). (Gk: pyr=fire) A yellow lustrus
(shiny) form of irondisulphide.
Pyroclastic: (Gk: pyr=fire; klastos= broken in
pieces) debris ejected from volcanoes.
Pyroclastic flow: also called glowing cloud or burning cloud.
An explosive volcanic eruption accompanied by rapidly expanding gas and
particles, travelling as a fluid gas down hill. Such flows are hot (up
to 1000ºC) and move at speeds of several hundred km per hour. They
are extremely dangerous.
Pyroxene: (Gk: pyr= fire; xenos= stranger) any
of a group of minerals commonly found as componenets
of igneous rocks, composed of silicates of
calcium, magnesium and iron.
Quartz: (Gk: Quarz) a mineral form of silica that crystallises
as hexagonal prisms.
Regolith: (Gk: rhegos= rug, blanket) Unconsolidated solid
material (residue) covering the bedrock of a planet. The basal layer of
soil, composed of material that is still recognisable as weathered rock
or other geological deposits (such as alluvium).
It grades upwards into overlying subsoil.
Regression: (L: re/red=back/again; gradi=step;
movement) a seaward shift of the shore, due to a fall in sealevel, a rise
of the land or sedimentation.
Resource consent: permit issued by a district or regional council,
allowing a change in the use of land (or other resources). Consents are
only required if a district or regional plan identifies the proposed use
as capable of causing adverse environmental effects.
Retirement: (Fr: rétirer= to withdraw) fencing
of land to exclude grazing by stock. It may entail rank grass and weed,
or reversion to scrub, or plantation of timber trees on the land that is
no longer grazed.
Reversion: spread of indigenous scrub across land that
is lightly grazed or retired from grazing.
Rhyolite: (Gk: rhyax= lava stream; lithos= stone)
a fine-grained volcanic rock of granitic
Rift: (of Scandinavian origin) a cleft or fissure; a trough
between two fault zones, with a down-dropped central block. It is often
the beginning of continental breakup and also occurs on mid-ocean ridge
Rilling: erosion of surface soil particles by rainwater running
off across the ground as distinct rills after heavy rain.
Riparian: (L: ripa= bank) pertaining to river banks.
Rock: rock is an aggregate of one or more minerals.
Rubification: (L: rubidus=red) when soil is thoroughly
dried from time to time, precipitates of iron and organic matter cannot
accumulate and the organic matter disappears by decay, causing irreversibly
dehydrated iron sesquioxides to form. Soils are called cinnamonic (red).
Runoff: water flowing across or through soil after rain. The
term is sometimes also applied for water flowing in ephemeral
Sandstone: a sedimentary rock composed
of sand grains, compacted and weakly cemented by a small quantity of lime.
Saturation: (L: satur= full) penetration of all the pores
and fissures in soil by water, so that air is excluded.
Schist: (L/Gk: schistos=split) a metamorphic
rock that tends to split into sheets or slabs, showing glistening or speckled
surfaces. It often has white bands of quartz alternating with bands of
fine-grained minerals, coloured silvery grey, greenish or pinkish.
Scour: erosion of channel beds and banks by stream flow.
Sediment: (L: sedere=to sit) matter that settles to the
bottom of a liquid.
Sediment load: the quantity of sediment passing a stream reach
in the course of a year.
Sedimentary rock: (L: sedere=to sit) rock laid down by
erosion. Matter that is carried by water or wind and deposited on the surface
of the land, and may in time be consolidated into rock. Under heat and
pressure, sedimentary rock may metamorphose.
Segregation of iron in soil: (L: segregare= to set apart)
in soils rich in iron but poor in two-layer clays that retain it, iron
tends to segregate, forming irregular concretions and nodules that become
hard as stone. See also ferrugination.
Serpentine: (L: serpentinus= serpent) a soft rock mainly
of hydrated magnesium silicate (Mg,Fe)3Si2O5(OH)4. Antigorite, a
flaky variety, is found in massive rocks. It is usually dark green and
sometimes mottled or spotted like a serpent's skin, taking a high polish
(greasy/silky lustre and a slightly soapy feel) and used as a decorative
material. Such serpentine is used as ornamental stone called verd antique
or serpentine marble. Chrysotile, a fibrous variety of serpentine,
is the most important type of asbestos. Serpentine
is also used as an additive in making magnesium superphosphate fertiliser.
Sesquioxides: (L: semi=half; qui=and; one and
half unit, 1.5) the hydrated oxides of iron, aluminium, manganese and titanium.
Three oxygen atoms for two metal atoms, like Fe2O3.
Shale: (German: schale=scale, plate) a fine-grained sedimentary
rock formed from silt and clay, tending to separate in thin sheets
along depositional bedding planes. Often contains organic matter like oil.
Sheetwash: erosion of surface soil particles by rainwater running
across the ground as thin sheets after heavy rain.
Shield: A large rigid area of the earth's crust, usually of
Precambrian rock (basement rock), which has been unaffected by later orogenic
(mountain building) episodes.
Shield basalt: A basaltic lava flow that erupted from numerous
small closely spaced vents, and coalesced to form a single unit. It is
generally of smaller extent than a plateau basalt (flood basalt).
Shield volcano: A broad, gently sloping volcanic cone of flat
domical shape, built chiefly of overlapping and interfingering basaltic
Silica: (L: silex=flint) silicon dioxide (SiO2) occurring
as quartz, etc. and as a principal constituent of sandstone and other rocks.
Silicate: (L: silex=flint) any of the many insoluble
compounds of a metal combined with silicon and oxygen, occurring widely
in the earth's crust.
Silviculture: (L: silva= a wood) management of timber
trees to improve their quality and yield, principally by pruning, and thinning.
It also entails seedling selection, fertilising, spraying or disease &
Sillimanite: (Named after B Silliman, an American chemist,
who died in 1864) an aluminium silicate occurring in orthorhombic crystals
or fibrous masses.
Smectite: an amorphous clay formed from easily weatherable volcanic
ashes, lava or basalt.
Soil conservation: measures which protect soil from excessive
erosion, structural breakdown, nutrient loss or pollution, thereby minimising
soil decline in its capacity of supporting plant and animal life.
Soil nutrients: minerals in the soil that are beneficial for
plant growth, principally the elements N, P, S, Ca, Mg, K and their derived
Soil structure: the arrangement of soil particles and inter-particle
spaces (pores and fissures). Good soil structure is beneficial for aeration,
percolation of water, penetration by plant roots, resistance to stock treading
and for load-bearing (tractor) when cultivated.
Solid solution: composed of various components such that the
chemical formula of the rock is not unique and any combination is possible.
Two or more elements can substitute for each other completely. For example,
the anions Mg++ and Ca++ , which are similar
in size and function, can combine CaSiO3 and MgSiO3 to (Ca,Mg)SiO3 as if
the rock components were dissolved into one another. The fact that silicate
rocks allow for substitution makes them easy to take apart through weathering.
Solonisation: (?) sodium-saturated soils (solonetz) having a
richer clay horizon at depth than at the surface.
Solum: (?) the horizons of the soil which have been changed
from the parent material by the soil forming process. Subsoil+top soil.
Solute load: (solute= a dissolved substance) the quantity of
dissolved chemicals passing a stream reach in the course of a year.
Spaced planting: plantation of trees, sufficiently apart that
a close canopy cannot form. Depending on species, mature trees at a density
of 50 to 100 stems a hectare are widely enough spaced for pasture or other
vegetation to grow in between.
Spar: (Old-English: sparen= plaster; sparstan=gypsum)
any crystalline, easily cleavable and non-lustrous mineral, e.g. calcite
Spinel: (?) MgAl2O4 a magnesium-aluminium oxide.
Spodosols: (?) see gleisation.
Soils with a light, ashy gray A horizon, and
a B horizon containing inorganic matter and clay leached from the A horizon.
Stadial: (Gk: stadion=stage) a colder phase within a
Staurolite: (?) an iron-aluminium silicate Al4Fe[O/OH/SiO4]2.
Stone line: ? the layer of stones found underneath the A-horizon,
caused by worms and other soil organisms rotating the soil above it.
Strata/stratum: (L: sternere= to strew; stratum=
something laid down) a layer or set of successive layers of any deposited
Stratovolcano: (L: stratum=layer) These are steep volcanic
cones built by both pyroclastic (thrown by
fire) and lava-flow eruptions. They are composed
of volcanic rock types that vary from basalt
to rhyolite, but their composition is generally
Stratovolcanoes may erupt many thousands of times over life spans of millions
of years. A typical eruption would begin with ash explosions and end with
extrusion of thick viscous lava flows. The cone-shaped form begins gradually
and becomes steeper (up to 35°) toward the summit, which generally
contains a crater. At the end of its activity, lava may gently pur out
to form a shield of rock (shield volcano).
Streamflow: water flowing through premanent channels.
Strike-slip fault: a fault along which the displacement of rock
bodies is horizontal.
Subduction: (L: sub=under; ducere= to lead, bring)
the process by which an oceanic plate slips underneath another plate.
Subsoil: (L: sub=under; solum= ground) the mineral-rich
layer of the soil, lying underneath the topsoil
and above the regolith, from which it is derived.
It is weathered to a stage where the parent material (rock
or sediment) is no longer recognisable.
Superphosphate: the most common form of phosphate fertiliser.
Suture: (L: sutura=a stitch; suere= to sew) a
join or weld left from a former collision of two continents.
Talc: (L: talcum; Arabic: talk) any crystalline
form of magnesium silicate that occurs in soft flat plates, usually white
or pale green in colour and used as a lubricator.
Tectonics: (Gk: tektonos= carpenter) originally, the
art of producing pleasing buildings. The study of large-scale structural
features. The study of the movement and deformation of the earth's crust
Tephra: (Gk: tephra= ash) loose material, e.g. ash and
deposited by volcanic eruptions. Tephra is
subdivided into three main particle sizes: less than 2mm = ash;
2-64mm= lapilli; over 64mm= blocks or bombs. Consolidated
ash is also known as tuff. Scoria is dark-coloured tephra,
which has been erupted but not in a molten condition. It is permeated by
holes from which gas has escaped, and in colour resembles cinders or slag
from a furnace. Pumice is a light coloured equivalent. Tephra is
usually dispersed widely during an eruption, depending on particle size.
Tephra can be accompanied by emissions of poisonous chlorine and fluorine
Terrace: (L: terra= earth) a flat to gently sloping alluvial
surface, elevated above floodplain level.
Tetrahedron/tetrahydral: (Gk: tetra=four; hedron=
seat) substance (crystal) contained within four equilateral triangles.
Tholeiite basalt: A basalt resembling that found in Tholey,
Germany. It is characterised by the presence of orthopyroxene
and/ or pigeonite in addition to clinopyroxene
and calcic plagioclase. Olivine
may be present.
Till: (origin unknown) chaotic mix of stiff clay, sand and boulders
deposited by glaciers during the last ice age.
Topaz: (L: topazus; Gk: topazos) a transparent
or translucent aluminium silicate mineral, usually yellow, used as a gem.
Topsoil: the uppermost layer of soil, rich in organic matter,
incorporated from the decay of plants and the activities of micro-organisms,
intermixed with mineral material derived from the underlying subsoil.
Tor: (Old-English: torr= broken hill) a broken hill or rocky
Torrent: (L: torrens= scorching, boiling, roaring) a
steep, permanently flowing channel, incised on a mountain slope.
Transform fault: a fault with horizontal movement connecting
two segments of a mid-ocean ridge. More broadly, a plate boundary along
which plates move horizontally past one another without either convergence
(coming together) or divergence (moving apart).
Transgression: a landward move of the shore, produced by a sea
level rise or sinking of the land. Erosion of the shore does not normally
cause significant transgression.
Translocation: movement from one place to another.
Tuff: (L: tophus; Italian: tufo) a volcanic
sediment, made of compacted debris
from old volcanic ash showers. See tephra.
Tundra: (of Lappish origin) a vast, level, treeless Arctic region
with a marshy surface and underlying permafrost.
Tunnel (Under-runner): a natural sub-surface cavity formed by
runoff flowing downslope through sub soil in heavy rain.
Ultisols: (?) soils similar to alfisols,
but with weathering more advanced. They include some lateritic
(highly leached) soils. See rocktable/soils.
Unconformity: a surface separating two beds of sedimentary
rock and representing a gap in time during which sedimentation ceased
or erosion removed the rock record.
Underthrusting: a process pushing one rock body underneath another
along an inclined fault plane. It is usually accompanied by intense deformation
and some metamorphism, and is common at the
collision edge of two plates.
Vermiculite: (L: vermiculari= be full of worms; vermis=worm)
a hydrous silicate mineral occurring as layered flakes. It resembles
the mineral mica. Vermiculite consists
mainly of the chemical elements aluminium, iron, magnesium, oxygen, and
silicon. It may be brown or yellow. When expanded by heat, vermiculite
becomes a lightweight, fireproof substance with good heat insulating properties.
It is used chiefly in building materials for insulation and soundproofing.
It is also used as a soil conditioner and potting material.
Vertisols: (?) soils with upper layers mixed or inverted because
they contain expandable clays (that swell when wet and crack when dry).
Volcanic: (L: Volcanus= Vulcan, Roman god of fire) produced
by a volcano.
Weathering: breakdown of rock or other geological
materials (e.g. alluvium) into soil, by physical
disintegration and chemical reaction.
Windblow: erosion of surface soil particles by strong wind blowing
across sparsely vegetated or bare ground.
Wollastonite: a calcium silicate CaSiO3.
Xerophytic: (Gk: xeros=dry; phyton=plant) drought
resisting plants, able to survive water shortage.
Zircon: a zirconium silicate ZrSiO4 of brown to grey colour.
Some translucent varieties are used as gemstones.
Zeolite: (Gk: zeo= boil; lithos= stone) is any
of a group of crystalline mineral compounds whose framework of atoms forms
microscopic tunnels and rooms. The internal structure of zeolites,
consisting of equal-sized channels, makes them useful as filters (molecular
sieves) and catalysts. Zeolites, one of the
most abundant kinds of minerals, are made of silicon, oxygen, and aluminium
and other metals. Used for oil refining, adsorbents, water softening, cosmetic