God for us to design products, we are the porters of nature!
aa Lava;
Pronounced ‘ah ah’ lava, it is believed to have developed in Hawaii through the sound one may make when trying to cross it in bare feet. It is a jagged angular, type of rock left from volcanic lava. Also known as clinker type lava.
Absolute age;
The dating of rocks, fossils and periods in the strictest sense, rather then relative.
i.e. A rock/fossil is 60mya, not the rock/fossil comes from the Palaeocene era
Acid;
Primarily a chemical term, that applies to any liquid with a Ph level less than 7
7 is neutral, above 7 is alkali/alkaline. Also used in conjunction with various geological terms in relation to % of silica included.
Acid Lava;
Lava that is rich in Silica content. It has a high melting point, usually above 850oC, thus it usually cools quite quickly upon exposure. Also very viscous, thus it is sticky and flows slowly.
Acid Rocks;
Igneous rocks containing high amounts of Silica. Definition of levels vary depending on regional learning, usually around 66% or more of Silica, often also considered to have 10% or more of free quartz.
Actinometer;
An instrument designed to measure solar radiation.
Active Fault;
A fault or faultline where movement is measured regularly.
Aftershock;
Movement from seismic activity, relative to that which caused an earlier earthquake; usually only minor by comparison to the main earthquake, and can be several days, even weeks later. It is usually generated from or near the original epicentre of the earthquake.
Age;
An interval of geologic time; can be related to absolute, relative or chronological terms.
Aggregate;
A mass or cluster of particles usually of similar sizes. Most commonly used in relation to soils and smaller sized rock.
Alkali (alkaline);
Primarily a chemical term, that applies to any liquid with a Ph level above 7
7 is neutral, above 7 is alkali/alkaline. Also used in conjunction with various geological terms in relation to % of silica included. Sometimes (although incorrectly) called base liquids.
Alkaline Flats (alkali flat) ;
A dry lakebed consisting of alkaline sediments; usually caused by intense evaporation.
Allotriomorphic (anhedral, xenomorphic);
Crystals within igneous rocks, not bound by their own normal crystal shape, but have had their outlines impressed upon them by surrounding crystals and adjacent minerals; i.e. a crystal that appears to be deformed by the shapes surrounding it.
Alluvium;
Deposits of sedimentary material caused by the actions of rivers and streams; including those laid in river channels and floodplains, but not those in lake or marine environments.
Alp;
A topographical term for a high-altitude shoulder or bench that lies above the glaciated troughs of a mountain range.
Alpine;
A collective or descriptive term for any high mountains. Quite commonly includes areas of permanent snow or glaciers.
Alpha Rays (alpha particles);
Electromagnetic waves composed of helium atoms with a double positive charge (He 2++). The alpha particles are relatively large and as a result, not very penetrating and are easily absorbed. A sheet of paper or a 3-cm layer of air is sufficient to stop them
Alteration;
Used as a geological term to describe changes in mineralogical composition of a rock; typically used to describe changes brought on during hydrothermal actions as part of metamorphism.
Amorphous;
Non-crystalline structures of a set chemical composition; minerals that do not form crystal structures, despite a set chemical composition. i.e. opal.
Amphibole;
Minerals of the ferromagnesian silicate group. i.e. hornblende.
Analogue:
In general terms, the similarity or familiar features shared by apparently unlike objects.
Andesite;
A fine grained volcanic rock of intermediate composition; approx 52-63% Silica. Named for the origin in which it was first observed, the Andes mountains.
Angle of Rotation;
The turning of an object or crystal system by an angle about a fixed central point.
The magnitude of the angle is the "amount of rotation" that separates the two rays; it can also be described as the measurement of a circular arc between the two rays when the angle is rotated.
Anhedral; see Allotriomorphic.
Anion;
One of the outer particles that surround an atom and carries the negative charge.
Anisotropic;
Used to describe a crystal that displays different properties in different plane directions; for example Kyanite, which can show a hardness of 6-7 crosswise and 4-41/2 lengthwise.
Anticline;
An arched fold or upfold in rock layers where the two outer limbs dip in opposite directions; the top of an arch or fold in rock layers.
Apparent Dip;
The angle between the horizontal and tilt directions of the bedding plane; can be measured in any direction except 90o to the strike and will always be less than the value of the true dip.
Archaean (Archean);
A term used to describe several different contexts of geological time. Generally of Pre-Cambrian times; approx 2500-3800mya.
1. Some regard as equivalent to Archaeozoic era.
2. In USA, only two eras are recognised for the Pre-Cambrian, this being the second era.
3. Originally thought to refer to any rocks in the Pre-Cambrian era, older than the Proterozoic.
Archaeozoic;
1. Specifically the second of three eras in the Pre-Cambrian times. see Archaean.
2. In general the entire Pre-Cambrian era.
Arenaceous;
A sedimentary rock, containing sand or having a sandy texture. Cementing particles range in size from 0.062mm to 2mm. A term usually given to describe sandstone rocks and quartzite, amongst others.
Argillaceous;
A sedimentary rock composed largely of clay
Arid;
A climatic region generally devoid of moisture and regular rainfall. Statistically denoted as an area that receives less than 250mm annual rainfall. Also one where evaporation rate exceeds the rate of precipitation.
Arkose; see Arenaceous
Artesian Basin;
The term comes from the basin of Artois, in north-west France.
A syncline or trough of permeable rocks with outcrops at the outer crests. Water seeps into this aquifer, moving towards lowest levels. Eventually the rock becomes saturated and the water is under pressure. If a borehole is sunk at depth to tap the water, an artesian well forms from which the water will initially flow upwards without pumping.
Associated Minerals;
Minerals that commonly appear with the mineral being described. These can often be regional or only relative to a particular mine, although many minerals are found in association purely through common chemistry and formation.
Asterism;
A property where by a crystal reflects the appearance of a star, usually when cut and/or polished.
Sapphires and Rubies are among the most famous of these. The shape appears due to either the presence of small inclusions or the internal chemical bonding of the crystal, depending on the type of mineral.
Atom;
The smallest particle of an element, it is surrounded by anions and cations, from which it gains its charge.
Atterberg Scale;
A grading scale used to classify sediments into subdivisions.
Augen
Originally taken from a German term ‘Ochsenaugen’, for which there is no direct mineralogical or geological translation. Augen is posted as meaning a large, lenticular eye-shaped mineral grain, aggregate or shape visible in metamorphic rocks.
Authigenic;
A phenomenon or characteristic that has formed in situ; i.e. calcite that has formed on shell fragments of a sedimentary layer, without metamorphism.
Automorphic (euhedral);
Minerals or crystals within igneous rocks that are bound by their own crystal form; i.e. they show their correct shape, without interference from surrounding minerals and crystals.
Axis of Symmetry (rotation axis);
An imaginary line running through the midpoint of a crystal, which when turned at a certain angle (angle of rotation) produces a position identical the original starting point. The axis can be called twofold, threefold, fourfold or sixfold symmetry, depending on how many times it must be rotated in order to bring about the identical position.
Basal Complex;
Generally regarded as the rocks which make up the shield type areas of the Pre-Cambrian deposits.
Basal Pinacoid;
A face on a crystal that are perpendicular to the ‘C’ axis, in an open end type form it may be both a base and top or ‘cap’ which closes the crystal, when a crystal end includes a point then it can only relate to the base of the crystal.
Basic Rocks;
Igneous rocks that are free of quartz and contain an average of 45-55% silica; also known as ‘Mafic’ or ‘Basaltic’ rocks.
Batholith (basthylith);
A large intrusive igneous rock (usually granite), with no apparent or observable base, it may be seen at the surface as a single pluton or several plutons together linked at depth. There are varying theories as to the development of Batholiths.
Bed;
The smallest (or to some the lowest layer) of stratified sedimentary rock which can be divided from its adjacent layers.
Bedding Plane (bedding layer);
The surface which separates one layer of sedimentary rock from the next; also indicates the break in deposition of sediment and rock.
Bedrock;
The base rock which remains relatively unweathered under layers of soil and weathered rocks (Regolith).
Bench;
A narrow relatively flat ledge or step, bounded above and/or below with steep slopes, usually associated with levels in an Open-cut mine; it can however also relate to a natural occurrence with such an appearance.
Beta Rays (beta particle);
The beta particle is an energetic electron given off by the nucleus of unstable isotopes to restore an energy balance; although much smaller than alpha particles, they can be stopped under normal situations by an aluminium sheet a few millimetres thick or by 3 metres of air.
Bi-pyramid (bi-pyramidal);
A crystal that forms symmetrically to form what appears as two pyramids joined at their bases; often seen in wulfenites from Whim Creek, Western Australia.
Birefringence (double refraction);
Used to describe light that is split into two paths, perpendicular to each other when the light is passed through an object; the most famous appearance of Birefringence is with a perfect (or near perfect) crystal of calcite is placed upon writing or drawing and two identical images can be seen through the crystal. Also see Double spar.
Black Smoker; see Fumaroles
Block Lava; see aa Lava
Borehole;
A hole drilled into the earth’s surface for exploratory use; mining companies use a series of these in an area to ‘prove’ a lode of mineralisation before actually mining.
Breccia;
Originating in Italian, the term relates to rock consisting of angular fragments in contrast to rounded fragments (conglomerate).
Brittle;
If a mineral specimen breaks into small (often irregular) pieces easily when penetrated by a sharp object, it is considered to be ‘Brittle’. A term used to help describe the physical properties on a mineral or rock specimen.
Butte;
Originating in France, it is used a term to describe a relatively flat-topped hill with steep sides, usually the top layer is very resistant to weathering and erosion preventing the breakdown of the structure. A smaller version of a Mesa, which it otherwise resembles.
Cainozoic (Cenozoic, Kainozoic);
Originating in Greek, meaning ‘recent life’; used to describe the third of the geological eras. Was first used as being synonymous with Tertiary; i.e. succeeding the Mesozoic but prior to the Quaternary. Now used to include the Quaternary and is divided into two periods, the Tertiary and Quaternary and thus includes all the Epochs from Palaeocene to Recent.
Calcareous;
Pertaining to high amounts of CaCO3.
Calcareous Rocks;
Sedimentary rocks containing high amounts of CaCO3.
Calcrete;
A sedimentary rock/deposit formed by the rise and evaporation of CaCO3 thru the upper layers of soil; deposition of solution then hardens through evaporation in a continuous cycle producing a hardened/rock feature.
Caldera;
A large circular type depression caused through volcanic activity.
1. By destruction of upper part of volcano through an eruption of great force.
2. By collapse of a volcanic cone inwards.
3. Gradual reduction of the outer areas of an extinct volcano.
Cambrian;
The first (earliest) of the periods of the Palaeozoic era, approx 490-545 to 510-570mya, depending on the chart you view.
Cap rock;
The hard layer of resilient rock that lies at the top of a hill or summit (Butte, Mesa), that protects the underlying softer strata; also used to refer to the impermeable rock that covers/caps an oil deposit.
Carbonaceous;
Mainly or largely composed of carbon based material; coal is considered carbonaceous.
Carbonates;
A group of minerals whose base ionic complex is CO3--
Carbonatite;
An intrusive carbonate rock usually associated with alkaline igneous activity.
Carboniferous;
A period of the Palaeozoic era, following the Devonian and prior to the Permian; approx 290-360 to 300-360mya. In USA it is further divided into the Mississippian (Lower Carboniferous) and Pennsylvanian (Upper Carboniferous). The European division is by two sub-systems that are further divided again, too complicated for this entry. Economically it is the most important era as it contains the largest percentage of the world’s coal supplies and large amounts of oil, oil shale, iron ore and fire clay.
Carboniferous Limestone;
First described in the UK as limestones of the Carboniferous era, yet the area concerned also contains sandstones and shales of the same era; often used today to describe CO3 rich limestone.
Carbo-Permian;
The end of the Carboniferous and beginning of the Permian, marked by the Hercynian Orogeny in the northern hemisphere (Eurasia) and by glaciation in the southern hemisphere (Gondwanaland); the Hallett Cove glaciation is of this period.
Cation;
One of the outer particles that surround an atom and carries the positive charge.
Chemical Weathering;
Breakdown of rock by chemical processes like oxidation (rusting) and hydrolysis (rain, rivers etc); processes that alter the chemical makeup of the rock upon exposure.
Cinder Cone;
A hill of conical shape that surrounds a volcanic vent, formed from the accumulation of fragmented lava which has solidified as it flew through the air. Cinder cones are most commonly made of scoria (glassy fine grained) material ranging in diameter from 3-4mm.
Clast;
1. An individual part of a sedimentary rock made from the breakdown of a larger mass.
2. A piece of fragmented rock resulting from a volcanic eruption.
Cleavage (cleavage angle);
The tendency of a rock or mineral to split or break along the planes determined by its crystallographic structure; used to help determine mineral species and physical properties.
Cleavage Plain;
The plane on which a rock or mineral breaks.
Clinometer;
An instrument used to measure angles of surface slope and dip in rock faces, bedding planes etc.
Columnar Lava (columnar structure);
A basaltic lava which has split along vertical planes through contraction while cooling; one of the most spectacular displays of which is the ‘Giants Causeway’, North Ireland.
Compound;
A substance made up of two or more chemical elements.
Conchoildal Fracture (concoidal fracture);
A fracture in a rock or mineral that produces a relatively smooth curved surface shaped in a similar fashion to the inside of a shell; used to help describe the physical properties of a mineral or rock.
Concretion;
A semi-rounded concentration of material that is harder that the strata it is found in; believed to be formed in the same manner as Calcrete.
Conglomerate;
A sedimentary rock consisting of sub-rounded to rounded fragments of rock, pebbles or cobblestones, cemented together by a finer matrix, like sand, silica or calcium carbonates.
Contact Metamorphism;
A type of Metamorphism created by the contact of country rocks with extruding or intruding Magma; the heat from the Magma literally melts the contact rock and allows Metamorphism though the heating and cooling of the rock. It can create new minerals or just alter the form of those already present.
Contact Rock;
Rocks that are affected by and/or show the properties of Contact Metamorphism.
Continental Crust;
A part of the earth’s crust that contains the main continental regions as apposed to Oceanic Crust. Generally thicker that the Oceanic Crust but can range from a possible 25km to as much as 70km+ thick under mountain belts.
Continental Drift; see plate tectonics
Corallian;
Refers to a deposit of limestone in the UK, which was deposited during the Jurassic period; also used previously in the UK to describe the same geological time period.
Craton (kraton);
A large section of the earth’s crust that has remained relatively unaffected by orogeny and similar formations, usually since the Pre-Cambrian. Often these areas are home to shield bedding forms and/or artisan basins.
Cretaceous;
The final (third) period in the Mesozoic era, it follows the Jurassic and precedes the Cenozoic era (or Palaeocene) which contains the Epochs. Approx 66.5-145
Cross Bedding (cross stratification);
The deposition of sediments that show (normally regular) change in direction of depositing, usually caused through the changes in either wind or water-flow while sediments are being deposited.
Cryptocrystalline;
A crystalline rock where the grains are so small they can only be viewed under magnification, usually with a high powered microscope.
Crystal;
A three dimensional body of a mineral that displays the regular form associated with the internal growth of the mineral’s chemical composition.
Crystal Classes;
Classes based on symmetry and geometrical shapes that are used to classify minerals.
Crystalisation;
1. The point in time at which a mineral begins to form a crystallised shape.
2. A term used to loosely describe the forming of a crystal from liquid form to a finished solid structure.
Crystalline;
A rock or mineral whose crystals have not formed to a large size and are compacted tightly together forming what appears as a lot of small fragments of the same/similar size/shape in order to produce a larger rock or mineral.
Crystallography;
The study of the crystal systems associated with minerals, it includes their nature, cause and atomic structure amongst others.
Crystal System;
The system used to classify minerals based on which Crystal Class their form takes. It is generally regarded that there are seven Crystal Systems.
Dacite;
An extrusive fine grained ‘glassy’ igneous rock of volcanic origin, which is composed mainly of Plagioclase and free silica or Quartz, with lesser amounts of ‘dark’ coloured minerals. The extrusive equivalent of Diorite.
Dendrites (dendritic form);
Skeletal forming crystals that develop from supersaturated solutions, usually forming on rock surfaces or in fractures and cracks in rocks; the most commonly known being Manganese Oxides.
Deposit; see Ore Deposit
Deposition;
The laying down of Sedimentary particles, soils or rock fragments in a bed like fashion. Most commonly on the base of lake beds and ocean floors. Although can be on surface areas with air contact rather than water; i.e. wind blow sands deposited in a gully.
Detritus;
Any loose material removed from rocks via physical and mechanical weathering or abrasion.
Devonian;
The forth and final period in the Paleozoic era, from approx 405-362mya.
Diamagnetism;
A term given to substances that show no signs of magnetism.
Diatreme (pipe);
A circular volcanic vent formed by high energy magmatic gasses, usually later, filled in by plutonic igneous rock; famous for having included diamonds in the hardened final product.
Differentiation:
In geological terms, a process where a single parent Magma assumes two (or more) different end compositions as it solidifies, also known as Magmatic Differentiation. In mineralogical terms, a rock or mineral that is segregated into bands during Metamorphism, also known as Metamorphic Differentiation, this is what leads to banding in Gneiss.
Diorite;
A course-grained, intermediate igneous rock of plutonic origin; with no more than 10% quartz present and a high percentage of Plagioclase feldspar and little darker coloured mineral. Also commonly known as black granite.
Dip (angle of dip, formation dip, true dip);
The angle that the fault plane or stratum makes to the horizontal plane, measured perpendicular to the strike of the bedding plane.
Dip Fault;
A fault line that has a dip almost perpendicular to the strike of the bedding plane, thus making it parallel to the true dip of the strata.
Disconformity;
A plane in the bedding where erosion has removed one or more levels of the bedding plane(s) before further deposition of sediment, thus leaving a ‘gap’ in the geologic record. Can be termed Angular Disconformity, Disconformity and nonconformity, depending upon the outline of the eroded surface.
Discordant;
Any phenomenon or item which does not conform to the normal order of things; a dyke cutting through a bedding plane or the foliation of country rock.
Dolerite (diabase);
A medium-grained, basic or Mafic (low in silica, high in dark minerals) igneous rock which intrudes in a Hypabyssal form; i.e. a dyke or sill.
Dormant Volcano;
There are two schools of thought here, a volcano which has not erupted in at least 10 000 years or a volcano which has not erupted in written history.
Double spar (Iceland spar, Iceland crystal);
A term given to extremely clear calcite that shows the property of Birefringence (double refraction).
Doubly Terminated (double termination);
A crystal that has grown freely at both ends, thus allowing a termination form at both, where there would normally be only one end terminated.
Dropstone;
A stone or rock that has been transported by a glacier for some distance and left in an area on different geological structure, thus appearing as if it does not belong, larger versions are known as erratics.
Drusy (druses);
A coating of small crystals over another mineral or rock; common species to form in this way include quartz and calcite. Often one can see the colouration and form of the mineral(s) below due to the thin nature of the coating layer.
Ductile;
A material capable of being stretched moulded or shaped to a relative degree without breakage.
Dyke (dike);
A thin plutonic or volcanic intrusion, commonly in a sheet like body, that cuts upward through bedding planes or country rock, rather than between then (a sill). Most dykes are of basaltic nature, in that they contain basic or Mafic (low in silica, high in dark minerals) magma.
Element;
1. A pure mineral made of only one type of chemical type; i.e. gold, silver, copper.
2. The chemical term describing a particle consisting only of an electron, neutrons and protons.
Eluvial Deposits;
Disintegrated mineral(s) material, that have usually remained close to their original source; commonly associated with gold deposits.
Endogenetic (endogenic);
Relating to processes originating within the earth, resulting in igneous rock formations.
Eocene:
The second Epoch in the Cenozoic Era; most important due to its diversity of fossil remains that relate to and link the present animal kingdom with its origins. Many firsts appeared during this time, including; whales, primates, monkeys and horses. Approx 34-56mya.
Eogene; see Palaeogene
Epicentre;
The point on the earths surface directly above the focus point of an earthquake.
Epimorph;
Crystal growth occurring on the surface of another mineral, often later having the inner mineral dissolve, leaving a hollow cast in the shape of the original mineral; one of the ‘psuedomorph terms’.
Era;
A geological time frame, consisting of one or more ‘periods’.
Erosion;
The removal of loose material from the earths surface, by means of wind, water etc; erosion takes place after weathering.
Erratic;
A stone or rock that has been transported by a glacier for some distance and left in an area on different geological structure, thus appearing as if it does not belong, smaller versions are known as dropstones.
Eruption;
The process of ejecting lava, gasses and solid or semi-solid material from a volcano.
Euhedral; see Automorphic.
Extinct Volcano;
A volcano that has not erupted in known history and appears to have totally ceased to function; re-awakening or new activity, has only been known on a few rare occasions where volcano’s were thought to be extinct.
Extrusion;
1. Emission of volcanic material at the earths surface.
2. A term used to describe a rock or bedding layer that has forced its way into an area of bedding from which it is not related.
Extrusive Rocks; see Volcanic Rocks.
Faceted;
A gemstone, mineral or rock that has been cut and polished in such a way, that its entire surface is made of planar surfaces.
Fathom;
A method of traditional measurement, used for depth, both at sea and in mines; i.e. a drive was cut at 45 fathoms to the second shaft, would in modern terms mean the drive was cut at a depth of 82.3m
Fault;
A rupture, fracture of crack within the rock strata of bedding lanes upon which displacement may be possible and/or visible.
Felsic;
Usually used to relate to light coloured igneous rock of high quartz/feldspar/silica composition or percentage; as opposed to mafic which has a high percentage or content of Fe, Mn and Al
Felsite;
Light coloured igneous rock of felsic origin.
Ferric (ferrous);
Of or containing Fe
Ferromagnetism;
A property of some substances, including iron and some alloys, in which application of a weak magnetic field within a specific temperature range induces high magnetism. Small discrete regions within the substance domains align with the direction of an applied magnetic field and produce the bulk magnetization.
Ferrous; see Ferric
Fibrous;
Describes a mineral that crystallizes in thin elongated threads, e.g. asbestos
Also used to describe alternate banding of sphalerite with marcasite and wurtzite.
Fissile Bedding;
Sedimentary bedding in which the rock will separate along the grain in laminar sheets.
Flotation;
A method used to separate minerals from excess rock after mining, ore is crushed and mixed in a suitable reagent which will allow the selected mineral to float to the surface when air is injected to the mix, the mineral is then skimmed from the mix and the excess removed.
Flow Till; see Glacial Deposit
Fluorescence;
A property of certain minerals that allow then to display luminescence when they are exposed to fluorescent light, also known as UV light; there are three main forms of UV light, long, medium and short wave, each denoted to the wavelength of the light waves emitted. Some minerals may fluoresce under all forms of UV, while other main only fluoresce under one or tow forms of UV.
Fluvial;
Of or relating to the effects of rivers.
Fold (folding);
Bend(s) in the rock strata or bedding planes, usually produced by deformation by the forces that also produce mountain ranges (orogeny).
Foliation;
Lamination or banding within a rock or bedding plane that is parallel to the schistosity. Usually these forms can be split along such planes.
Foreshock;
A form of tremor or small earthquake that foresees an earthquake proper or main shock.
Form;
The crystallographic shape in which a mineral should appear if it grows without external interference.
Fossil;
The imprint, trace or remains (altered or not) or an organic organism from our geological past that has been preserved in rock or the like. Other means of preservation known include ( but are not restricted to) tar pits and burial in ice.
Fracture;
A crack, joint or fault within a rock or bedding planes, similar to a fault, although not usually associated with movement.
Fumaroles; Latin fumus, smoke
Gabbro;
A course grained igneous rock regarded as the plutonic equal to basalt, which consists mainly of pyroxene, olivine and Ca-plagioclase.
Gamma Rays;
A light wave in the same electromagnetic family as light and x-rays, but is much more energetic and harmful. It is capable of damaging living cells as it slows down by transferring its energy to surrounding cell components. It requires heavy shielding; i.e. lead or concrete.
Gangue Minerals;
The additional valueless rock include with ore in mining. Often used to describe minerals such as baryte, calcite, fluorite, pyrite and quartz that are included in the ore materials.
Gemstone (precious stones);
Minerals that are of suitable colour, clarity and hardness to be used for the manufacture of jewellery.
Geocentric;
A term used to describe any model using the earth as its central point, early astronomers’ believed the solar system was ‘geocentric’, thus they believed the planets, stars and the sun, rotated around the earth!
Geode;
A hollow cavity within a single rock, often lined with crystals of a different mineralogical nature.
Geologic Time;
The scale of periods, eras and epochs (time frames), used to measure the geological history of the earth, its formation, appearance, mineralogy, fossils, evolution etc.
Geomagetism;
The magnetism of the earth, also relates to the study of the earths magnetic fields.
Geosyncline;
A major structural downfold in the earth’s surface that has since forming gathered large amounts of sedimentary and volcanic deposits.
Glacial;
Pertaining to anything related to a glacier.
Glacial Deposit (glacial till);
A till that has been deposited by glacial ice or glacial melts.
Glaciofluvial;
Directly translated means glacier river, it pertains to things related to the flows from or that include glaciers.
Gneiss;
A metamorphic rock made usually from shale, it is usually course grained and shows banding and crystallisation.
Gondwana
The southern portion of the great ‘super continent’ Pangea, often, but mistakenly, used in relation to Australia. While Australia was part of Gondwana, it also included South America, Antarctica, India and Africa, as well as other smaller regional areas.
Gossan;
A Cornish term for the ferruginous deposit, often having a ‘rusty’ colour, within the upper regions of a mineral deposit from which sulphides have dissolved or oxidised.
Graded bedding;
A sedimentary layer consisting of sorted particles/rock based on size, where the larger particles have settled at the bottom with decreasing size particles thru to the upper part of the layer.
Granite;
A plutonic igneous rock showing course crystallisation, commonly known for its (major) composition of quartz, K-feldspar and biotite, it is the most common of the igneous rocks.
Greenstone;
Any altered basic igneous rock that has a green colour as a result of the presence of chlorite, hornblende, epidote or similar.
Greisen;
A pneumatolytically altered rock (usually granite), consisting mainly of quartz and a green coloured mica, commonly associated with kaolinisation.
Greywacke; see Arenaceous
Habit;
Characteristic appearance of a given crystal form, often interchanged with the term ‘Form’, also used as a descriptive term to relate to the given local mineralisation of a deposit; i.e. the local habit has these minerals in association with crystal ‘x’.
Half-life;
The length of time given to take an atom to degrade/decay to half its original size or into another isotope.
Halides;
A group of minerals containing a principal ion of the Halogen series of elements; fluorine, bromide, chlorine and iodine.
Hardness Scale; see Mohs hardness Scale
HCl Test;
A wet chemical test in which a small particle/area of a mineral is exposed to HCl (hydrochloric acid) to help determine its chemical makeup. Most commonly known for creating the reaction of, large amounts of ‘fizz’, when placed on base carbonate minerals (calcite etc).
Heavy Minerals;
Not a heavy metal rock (and roll) group! Heavy minerals are those whose specific gravity allows then to sink in high density liquids, usually quoted as any mineral with a specific gravity or density of 2.9 or higher. Bromoform liquid is used as the base upon measuring this via floatation.
Holocene;
Meaning ‘the whole of modern life’, it relates to all of the time since the end of the Pleistocene. Approx 10,000-12,000 years ago until the present day.
Hornblende;
A mineral from the ‘Amphibole’ group, it forms a solid solution series, between various metals and has the generalised formulae of (Ca,Na)2(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2
Hornfels;
A fine grained metamorphic rock formed through contact metamorphism.
Hydrothermal Minerals (hydrothermal deposit);
Minerals formed from hot, aqueous solutions under pressure (often at great depth); this process forms both new minerals as well as metamorphic minerals, the later is through the dissolving and re-crystallisation of igneous or sedimentary rocks.
Hydrothermal Veins;
Fractures within rocks or bedding planes that have been filled with minerals formed through hydrothermal activity.
Hypabyssal Rocks;
Smaller scale igneous intrusions of magmatic origin that have solidified before reaching the earth’s surface; i.e. dykes and sills.
Idiomorphic Crystals;
Describes minerals that occur naturally in the form of fully developed crystals, where their growth has been unaffected by outside influences.
Igneous Rocks;
Rocks that have formed from magma or lava, they are classified according to their, crystal (grain) size, texture and chemical composition (percentage of silica).
Igneous Succession;
The classification system of igneous rocks.
Inclusions (embedded crystals);
Substances included inside a crystal or rock; i.e. rutile in quartz.
Index Fossil;
A fossil which can be found during a determined geological time frame, thus allowing for an accurate aging of the sediment or rock in which it is found.
Induration;
The process of hardening sedimentary deposits into rock, through heating, pressure and compression.
Inlier;
An (?circular) exposure of older rock that is surrounded by younger rock, the appearance of which is partially due to a faster rate of erosion of the surrounding younger rock.
Inselberg:
From german meaning ‘island mountain’. A large steep sided, flat top hill of solid rock that appears to rise suddenly from an otherwise ‘flat’ landscape. Arguably the most famous Inselberg in the world is Uluru (formally Aryes Rock), Northern Territory, Australia.
In situ;
From Latin, meaning; in its original position.
Interbedded;
A layer that is between two other layers; i.e. a layer of sandstone interbedded between a layer of shale and a layer of basalt.
Interglacial;
Pertains to the time frame between glacial periods or ice ages.
Ion;
An electrically charged outer particle that surround an atom and carries the negative charge.
Iron Hat; see Gossan
Isometric Crystals;
A group of crystals whose ‘normal’ shape would cover approximately the same area in all three directions. A crystal group.
Isostasy;
Uplift due to the buoyancy of the continental crust. Refers to the state of balance of the continental crust through leveling by compensation.
Isotopes;
Elements with the same number of protons in their nuclei, but a different number of neutrons; they have almost the same chemical properties and the same atomic number but a different atomic weight. Often related to C-14 carbon dating.
Isotrpisation;
The destruction of a crystal’s internal chemical lattice via intense radioactive bombardment.
JMA Scale;
A scale of earthquake intensity used by the Japanese Meteorological Agency; rating is from 0-12.
Joint;
A crack or fracture in rock or bedding that shows no discernable movement on either side.
Jurassic;
The middle period of the Mesozoic era; approx 145-200mya. It was during this period that the dinosaurs reached their largest sizes and has been made famous world wide by the movie ‘Jurassic Park’. It was the last period in which dinosaurs were present for both the start and ending; they reached extinction during the Cretaceous period, following the Jurassic.
Kaolinite (kaolin);
An aluminium silicate mineral that is produced through the chemical weathering and breakdown of feldspar rich igneous rocks, it is also a major constitute of kaolin clay, also known as ‘china clay’, from which the worlds most famous and fine china, pottery and ceramics have been made.
Kaolinisation (kaolinization);
The descriptive term to the process of chemical weathering and breakdown that forms kaolinite.
Karst;
A topographical landscape produced through the characterised sinkholes, depressions and underground caves produced by dissolution (usually via faults and cracks) of limestone, gypsum or dolomite in the upper most bedding layers.
Kimberlite;
A peridotite that has become brecciated (see breccia), it contains mainly mica and olivine as its main minerals, it usually fills a diatreme or pipe and are famous for having diamonds as inclusions. The Kimberley regions of Africa were named for the Kimberlite pipes in the area that have high content of diamonds. The Kimberley region in Australia was named after the African region of the same name.
Kratogen; the former spelling of kraton/craton.
Lava;
Molten rock (magma) that extrudes to the surface of the earth.
Leucocratic;
A term used to describe light coloured rocks; rocks with less than 30% dark minerals.
Lithification (lithifaction);
The processes by which sedimentary deposits are converted into sedimentary rock.
Lode;
A Cornish term for an area infilled with metalliferous ore(s).
Lustre;
From Latin ‘Lux’ meaning light; a reflective appearance as seen by the naked eye, used to describe the appearance of a mineral or rock.
Mafic;
A term relating to igneous rocks that have a high percentage of dark coloured minerals or Fe, Mn rich silicates and low percentage to 0% of quartz.
Magma;
Molten rock beneath the earth’s surface, from which either plutonic igneous rocks form or through extrusion becomes Lava.
Magmatic Differentiation; see Differentiation.
Mantle;
The middle layer between the earth’s crust and its core. Regarded as being approx 3480km deep.
Massive;
A term loosely used to describe a crystalline mineral that has not formed crystal faces, but can still usually be distinguished by normal methods. An adjective used for the description of an ore deposit.
Mechanical Weathering;
The physical breakdown of rocks, through actions like exfoliation, which do not in any way change the chemical makeup of the rock.
Melting Point;
The temperature at which a solid will begin to melt and become a liquid.
Melt Water;
The water that has melted from a glacier, often used to describe a stream or river that is fed by the melting waters of a glacier. One of the main release point for erratics and dropstones carried by the glacier as it has moved.
Mercalli Scale;
The scale used by most of the western world to measure the intensity of an earthquake, it was developed in 1902 by Giuseppe Mercalli. It ranges from 1-12 and is different from the Richter Scale which measures earthquake magnitude.
Mesa;
A Spanish term for a flat top hill or tableland, a larger version of a Butte.
Mesocratic (mesocratic rocks);
A term to describe intermediate igneous rocks with 30-60% mafic content.
Mesozoic;
From the Greek term meaning ‘middle life’, it is the middle era of the Phanerozoic Eon; approx 65-250mya, it is commonly known as the Age of the Reptiles.
Metamict Minerals;
A mineral exhibiting internal lattice disruption through radioactivity, while the normal external shape is still retained.
Metamorphic Differentiation; see Differentiation.
Metamorphic Rocks;
Rocks that have undergone change or development due to metamorphism.
Metamorphic Succession;
Classification of minerals and rocks that were created by Metamorphism.
Metamorphism;
Alteration or formation of rocks (usually at great depth), via heat, pressure and/or hydrothermal fluids.
Metasomatism;
The gradual change in rock structure caused by the natural replacement of chemicals through interaction with liquids or gases
Meteorite;
Any extra terrestrial rock or mineral body that lands upon the earth’s surface, they are typically high in Fe content and have considerable Ni and silicate contents.
Migmatite;
From the Greek ‘migma’ meaning mixed, it is a rock that shows mixed composition of crystalline structure, from an obviously previous molten material of a more or less granitic origin.
Micromount (micro);
A mineral specimen that requires some form of magnification in order to view and best appreciate it, although this does not need to be relevant to the overall size of the specimen; also a formal grade in mineral competitions, where there are also restrictions to the overall size of the specimen.
Miller Indices;
A three digit number used to designate crystal faces with respect to the co-ordinates of the crystal system.
Mineral;
A rock of which its makeup can be expresses as a single given chemical equation or formulae. Minerals normally form a shape known as a crystal, but can in some instances be Amorphous.
Mineral Deposit; see Ore Deposit.
Mineralisation (mineralization);
1. The term given to the formation of minerals though introduction or replacement into pre-existing rocks.
2. The conversion of organic matter to inorganic forms through the process of replacement; used to refer to the formation of some fossils.
Miocene;
An Epoch of the Tertiary period prior to the Pliocene; approx 5-24mya, it is believed that humanoids first appeared during this time and mammals became of large importance to the ecology to earth.
Mohs hardness Scale (Mohs scale);
An empirical scale designed to use ten minerals as key points to determine the relative hardness of a mineral or rock and consists of the following;
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
10. Diamond
Monochromatic;
Generally means of one colour, in minerals it can also mean a mineral whose colour characteristics remain virtually unchanged no-matter what the form or habit the mineral is found in; this is different to most minerals, as they vary according to local impurities and trace elements etc.
Moon;
Earths only permanent terrestrial body or satellite of natural origin, its rotation of the earth takes 27 days, 7 hours and 43.25 mins. It has the greatest influence on tidal motions and is found as an important entity in many cultures.
Moonstone;
A lustrous bluish-white semiprecious stone that is a translucent variety of plagioclase feldspar, often used for jewellery.
Moraine;
An acumination of rubble and debris that has been transported and deposited by a glacier; there are several forms of moraines, each relating to the sorting, placement and type of material deposited.
Mountain;
A natural large (usually steep sided) hill like form that rises considerably higher than the surrounding countryside, san be in a singular form or in a range, in geological terms a minimum height of approx 600m is required for a structure to be labelled a mountain in some countries, while heights of at least 2,500m are required in others. The terms Orogenesis and Orogeny are used to describe the way mountains, the study of mountains and the forces that form them is known as Orography, the highest point of any mountain on earth is on Mount Everest at 8,848 m.
MSK Scale;
A revised scale of earthquake intensity use primarily in Europe, as apposed to the JMA and Mercalli Scales.
Multicoloured;
A term generally used to describe any mineral or rock with more than one colour, can also (although rarely) used to describe a mineral that has variances in colour from one region to the next.
Native;
An adjective used to describe a metal in its pure form; i.e. native copper.
Nitrates;
A group of minerals characterised by the base ionic structure of NO3-.
Nonbrittle;
One of the terms used to help describe the physical properties of a mineral or rock, a specimen is considered Nonbrittle when particles remain on the edge of a groove or cut when the specimen is penetrated by a hard object.
Nonconformity; see Disconformity
Obsidian;
A jet black volcanic glass, it is extremely fine grained, usually of Rhyolite composition, thus it has a high percentage of silica (>65%). It forms from rapid cooling of the upper part of Rhyolitic lava flows.
Occurrence;
For some it refers to the preferential appearance of a mineral in a given type of deposit, to others it is simply a term referring to any locality which is listed for the collection of mineral specimens or mining.
Ocean-floor Spreading; (sea-floor spreading)Ochsenaugen; see Augen.
Oligocene;
The third Epoch of the Cenozoic era, following the Eocene and preceding the Miocene; Approx 24-35mya.
Olivine;
One of the basic rock building minerals, usually olive green to dark green in colour, with no cleavage and a hardness of 6 1/2-7; it is the major component of Mafic and Ultra-mafic rocks.
Opaque;
Meaning ‘not transparent’, it is used to refer to minerals and rocks that can not be seen through.
Open-cut Mining (open-cast mining, open-pit mining);
Mining by the use of a large open air pit, in which all the ore and surrounding material are removed before the ore is treated, rather than just taking ore. Very common in areas that are well away from major towns and cities, although some of the worlds most famous Open-cut mines are in fact quite close to major townships, most of these townships have been born of the need for localised housing and supplies.
Ordovician;
The second period of the Palaeozoic era, it was named from an ancient tribe which lived in the region of the North Wales and the Welsh borders; approx 445-490/500mya.
Ore (Ore Deposit);
1. A naturally occurring mineral aggregate of enough volume for economic use.
2. The metalliferous material of economic use taken from the earth though mining.
Ore Minerals;
Any mineral metalliferous or not, of economic importance that can be acquired through mining; often used to refer to minerals or a massive or crystalline nature, rather than those which have formed crystals.
Organic Weathering;
Biological processes that contribute to the breakdown of rock material into smaller pieces; usually one of the ‘physical’ weathering methods.
Orogenesis (orogeny);
In its original, literal sense, orogenesis means ‘mountain building’, but today it more specifically refers to the mountain building via plate tectonics (as opposed to mountain building by erosion).
Processes associated with orogeny include faulting, folding, metamorphism, plutonism and isostasy However, many topographical features of mountains – cirques, U-shaped valleys – are the result of non-orogenic processes, such as weathering, erosion, and glaciation etc.
Orthoclase;
Also known as K-Feldspar, it is one of the basic rock forming minerals; it is a light coloured feldspar and often a major constitute of granite,.
Orthogneiss; see Gneiss
Outlier;
A group of rocks or rock ‘outcrop’ which is separated from its main mass through weathering and erosion, leaving behind an young rock form surrounded by older rocks and/or strata.
Oxidation;
One of the methods of chemical weathering in which O2 reacts with the chemical makeup of the rock and forms new chemical compounds, usually of the oxide and hydroxide forms.
Oxidation Minerals;
Minerals that have been altered through the chemical reactions involving O2, normally at low pressures and at low depths, were there is the ability for the influence of external forces such as the atmosphere and groundwater.
Oxidation Zone;
The area or zone in a mineral deposit, in which minerals become Oxidised through the interaction with O and CO2.
Oxide Minerals (Oxides);
A mineral group which also includes Hydroxides and Halides, in which the main ionic form is O.
Palaeocene; Palaeogene; Palaeomagnetism; Palaeozoic (Paleozoic); Paragenesis; Paramorphism;
Structural alteration of a mineral without change of chemical composition. It involves the polymorphous alteration of a high-temperature form of a mineral to a low-temperature form. With paramorphism there is a rearrangement in the crystalline structure of the mineral without a change in chemical composition; the external shape of the original crystal is also preserved. Examples of paramorphs are hexagonal α-quartz after trigonal β-quartz, rhombic sulphur after monoclinic sulphur, trigonal calcite after rhombic aragonite, and cubic pyrite after rhombic marcasite.
Pegmatite; Penetration Twin; Peridotite;Perimorph; Period; Permian; Petrography; Phacolith (phacolite); Phanerozoic; Phantoms; Phenocryst;Phosphates; Phosphorescence; Physical Weathering; see Mechanical Weathering
Pillow Lava; Pinch Out; Pipes; Pitch; Placer Deposit; Placers; Plane of Symmetry; Plate Tectonics; Pleistocene; Pleochroism; From Greek pleo- (more) + -chroic (having a color)
Pleochroism is an optical phenomenon in which mineral grains within a rock appear to be different colours when observed at different angles, often seen when viewing under a polarizing petrographic microscope.
Pliocene; Plutonic Rock (pluton, plutonism); Pneumatolysis; Polymorphism; Porphyry; Pre-Cambrian; Primary Minerals; Prospecting; Pseudo-bedding;Psuedomorph; Pumice; Pure Substance; Pyroclastic Material (Pyroclastic rocks); Pyroxenes;
Quarry; Quartzite; Quartz Porphyry;
Traditional German name for rhyolite extrusions, or rocks containing over 65% silica but only 10% quartz, often found in old text.
Radioactive; Radioactive Decay; Radon; Rare Earths; Refractive Index; Regional Metamorphism; Regolith; Relative Age; Replacement; Retrograde Metamorphism; Rhyolite; Richter Scale; Roche Moutonnee; Rock;
Salts; Sand; Sandstone; Schist; Sclerometer (Turner-sclerometer);
Invented in 1896 by Prof. Thomas Turner, its name is derived from the Ancient Greek meaning for ‘Hard’
It is used to microscopically measuring the width of a scratch made by a diamond under a fixed load and fixed conditions.
Scree; Secondary Minerals; Sediment; Sedimentary Rock; Sedimentary Succession; Shale; Shear Fault; Shear plane; Silicates; Sill; Silurian; Skarn;Sluice; Soil; Solfataras;
An Italian term for fumaroles, vents and other areas that give off gases from an inactive volcano.
Specific Gravity; Specimen; Specimen of Convenient Size; Spherulites; from Greek sphaira = ball and lithos = stone. Radiating or globular aggregates that have developed out from their centre in all directions evenly within the available space. In petrology, they are small, rounded bodies that commonly occur in vitreous igneous rocks.
Stalactites; Stalagmites; Stratification; Streak; Streak Plate; Stope (stoping); Stratification; Structure; Subhedral;
A crystal within an igneous rock that has formed partially with its own crystal form and partially from the shape impressed upon it by surrounding crystals and minerals; a crystals that has formed half way between Automorphic and Allotriomorphic means.
Subvolcanic Formations; Successions; Sulphates (sulfates); Sulphides (sulfides); Syngenetic; Systematic Collection; Systems of Axes;
Tailings; Tarnish Colours; Tectonics; see Plate Tectonics.
Tenacity; Texture; Thrust-fault; Thrust-plane; Till; Tillite; Trace Elements; Trachyte; Transparency; Trunk; Twins (twinning); Type Locality; Type Species;
Ultrabasic rocks;
Unconformity;
Uniformitarianism;
Varieties; Vein; Venting; Volcanic Activity; Volcanic Efflorescences; Volcanic Rocks;
Rock resulting from volcanic activity at or near the earths surface.
Volcano; Vug (vugh);
Weathering; White Smoker;
Xenocrysts; Xenolith (xenolyth); Xenomorphic Crystals;
Zeolites; Zone Fossil; see Index Fossil.
Zoning;
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