| aa | | rough clinker like lava |
| aboral | | upper domed surface of an echinoid |
| abyssal (plain) | | relatively flat ocean floor generally 5km below the surface |
| acanthite | | silver sulphide mineral |
| accessory (minerals) | | minor constituents of an igneous rock |
| accidental (minerals) | | minerals not usually associated with a particular rocktype that may have been introduced by an intrusive magma |
| accretionary (prism) | | sediment scraped from a subducting plate |
| acheulian | | flint implements associated with early forms of homo sapiens |
| achondrite | | stony meteorite that has no chondrules |
| acicular | | needle shaped crystals |
| acme (zone) | | zone containing an exceptional abundance of fossils of the same taxon |
| acmite | | sodium iron silicate mineral |
| actinolite | | hydrous calcium magnesium iron silicate mineral |
| adamite | | hydrous zinc arsenate mineral |
| adductor (muscles) | | the muscles that draw together the two shells of marine molluscs |
| adit | | Horizontal tunnel into a mine |
| adularia | | potassium aluminium silicate mineral |
| aegirine | | sodium iron silicate mineral |
| aeolian | | deposits formed by sediments transported by wind or suspension |
| aerobic (decay) | | decay of organic matter in the presence of oxygen |
| aftershock | | seismic tremors that follow in the wake of an earthquake |
| agate | | silicon oxide mineral |
| aggregate | | a mixture of more than one type of rock or mineral |
| agmatite | | see migmatite |
| akermanite | | calcium magnesium aluminium silicate mineral |
| alabaster | | massive form of gypsum |
| albite | | sodium aluminium silicate mineral |
| alexandrite | | green gemstone form of beryl that appears red under artificial light |
| allanite | | rare earth silicate mineral |
| allochromatic | | a substance that can display a number of different colours |
| allochthonous | | a rock "foreign" to those normally associated with an area that has been moved there through fault action, wind or water |
| allotriomorphic | | microscopic texture of an igneous rock |
| allotrope | | element that displays different physical properties while sharing the same chemical composition |
| alloy | | mixture of two or more metals |
| alluvial | | sediment deposited by a river |
| almandine | | iron aluminium silicate mineral |
| alunite | | hydrous potassium aluminium sulphate mineral |
| alurgite | | hydrous potassium aluminium silicate mineral |
| amazonite | | blue green gemstone form of microcline |
| amber | | fossilised tree resin |
| amblygonite | | hydrous lithium aluminium phosphate mineral |
| ambulacrum | | radial plate in the test of an echinoderm, possessing pairs of pores |
| ameboid | | crystalline structure resembling an amoeba |
| amethyst | | silicon oxide mineral |
| ammonite | | an extinct marine cephalopod |
| amorphus | | non-crystalline mineral, ie opal, amber etc |
| amphibole | | group of metal silicate minerals |
| amphibolite | | metamorphic schist or gneiss comprised mainly of amphibole |
| amygdule | | crystals lining a cavity in a rock - see geode |
| anaerobic (decay) | | decay of organic matter in the absence of oxygen |
| analcime | | hydrated sodium aluminium silicate mineral |
| analogy | | similarities in fossils due to convergent evolution |
| analyser | | upper filter in a polarising microscope |
| anapsid | | reptile type where the skull contains no openings in the temple region i.e turtles |
| anatase | | titanium oxide mineral |
| anatexis | | large scale melting of rocks due to subduction - see continental drift |
| anatexite | | see migmatite |
| andalusite | | aluminium silicate mineral |
| andesite | | volcanic rock intermediate between basalt and rhyolite |
| andradite | | calcium iron silicate mineral |
| angiosperm | | generic term for flowering plants |
| anglesite | | lead sulphate mineral |
| anglian | | glacial period from c. 415,000 - 380,000 years ago |
| angular (discordance) | | a difference in dip displayed in the strata above and below an unconformity |
| angular (shear) | | change in the 90° angle on the planes of two intersecting bodies caused by distortion |
| anhedral | | crystals that do not display their usual form |
| anhydrite | | calcium sulphate mineral |
| anhydrous | | containing little or no water |
| anisotropic | | crystalline structure that is opaque to light |
| anisotropism | | variation in the physical properties of a mineral according to its plane |
| annabergite | | hydrated nickel arsenate mineral |
| anorthite | | sodium calcium aluminium silicate mineral |
| anorthosite | | igneous intrusive rock |
| anterior | | the front end of an animal |
| anthophyllite | | hydrous magnesium iron silicate mineral |
| anthozoa | | taxonomic class containing corals |
| anthracite | | the hardest form of coal containing 95% carbon |
| anticline | | a convex shaped fold |
| antidune | | bed produced upstream due to high current velocities |
| antiform | | structure seen in folded rocks similar in shape to an anticline |
| apatite | | hydrous calcium lead arsenic phosphate mineral |
| aperture | | the opening in a mollusc through which the foot extends |
| aphanitic | | texture of an igneous rock containing microscopic crystals |
| aphyric | | fine grained crystalline texture |
| aplite | | hypabyssal fine grained igneous rock |
| apophyllite | | hydrated potassium calcium silicate mineral |
| apophysis | | sill or dyke connected to a larger instrusive igneous mass |
| apparent (dip) | | apparent, as opposed to true, dip in a stratum |
| aptychi | | lower jawbone of an ammonite |
| aquamarine | | blue gemstone form of beryl |
| aquiclude | | strata impermeable to the passage of water |
| aquifer | | strata containing large quantities of water trapped within it |
| aragonite | | calcium carbonate mineral |
| archaeozoic | | era covering the period from 4000 to 2500 million years ago |
| arenaceous | | sandy |
| arenite | | consolidated wind/water borne fragments |
| arete | | sharp ridge between valleys in a glaciated area |
| arfvedsonite | | hydrous sodium iron magnesium aluminium silicate mineral |
| argentite | | silver sulphide mineral |
| argillite | | consolidated clay deposits |
| arkose | | consolidated feldspar eroded from it's parent rock |
| arsenopyrite | | iron arsenic sulphide mineral |
| artesian | | relating to water held underground in an aquifer |
| arthropoda | | taxonomic phylum that includes insects and crustaceans |
| articulate | | class of brachiopods where the shell valves are hinged by a tooth and socket arrangement |
| articulated | | description of a fossil found where joints, bones etc are complete as in life |
| artinite | | hydrated magnesium carbonate mineral |
| asbestos | | generic description for the fibrous mineral group that includes chrysotile, actinolite and crocidolite |
| asexual | | form of reproduction where only one parent is required |
| assay | | the analysis of minerals to determine their composition, purity etc |
| assemblage (zone) | | biostratigraphic zone consisting of several species whose ranges overlap |
| asterism | | starlike rays of light seen by refection from a polished mineral |
| asteroid | | small body orbiting the sun |
| asthenosphere | | lower part of the mantle |
| astrophyllite | | hydrous potassium iron titanium silicate mineral |
| asymmetric (fold) | | fold where one limb is markedly longer than the other |
| atacamite | | hydrous copper chloride mineral |
| augen | | texture of metamorphic rocks such as gneiss |
| augite | | calcium magnesium iron aluminium silicate mineral |
| aureole | | rock that has undergone thermal metamorphism through contact with an igneous intrusion |
| aurichalcite | | hydrous zinc copper carbonate mineral |
| authigenic | | a mineral formed within a sediment rather than deposited with it |
| autochthonous | | native to where it was found; where it was originally formed |
| autotroph | | organism that extracts carbon dioxide mineral from its environment |
| autunite | | hydrated copper uranium phosphate mineral |
| aventurine | | silicon oxide mineral |
| axial (plane) | | plane though the hinge of a fold |
| axial (rift) | | a steep sided valley along the centre of an oceanic ridge |
| axial-planar (cleavag | | plane in a fine grained rock where the cleavage is parallel to the axial plane |
| azoic | | old term for the Archaean era |
| azurite | | hydrous copper carbonate mineral |
| babingtonite | | hydrous calcium iron manganese silicate mineral |
| backshore | | part of a beach above the mean high tide mark that receives deposited material only during storm conditions |
| barchan | | crescent shaped sand dune formed by the action of wind |
| barite | | barium sulphate mineral |
| barrier (island) | | barrier formed by beach deposits that separate a lagoon from the sea |
| basalt | | black glassy volcanic rock |
| basanite | | extrusive igneous rock |
| basement | | ancient rocks underlying younger sedimentary strata |
| basic (rocks) | | igneous rocks containing a low proportion of silicon |
| basin | | the inner part of a syncline |
| batholith | | large plutonic intrusive body |
| bauxite | | hydrous aluminium oxide mineral |
| bed | | the smallest strata of a rock succession |
| bedding (plane) | | the junction between successive periods of deposition |
| bedload | | coarse sediment moved through action of turbulent water flow |
| belemnite | | an extinct tubelike cephalopod |
| benitoite | | barium titanium silicate mineral |
| benthic | | bottom dwelling aquatic organisms |
| bentonite | | grey-white clay formed from consolidated volcanic ash |
| berm | | flat area of beach standing just above the high water mark |
| bertrandite | | hydrous beryllium silicate mineral |
| beryl | | beryllium aluminium silicate mineral |
| betafite | | hydrous uranium titanium niobium oxide mineral |
| BGS | | British Geological Survey |
| BIF | | banded ironstone formation of alternating layers of chert and haematite |
| biogenic | | formed by biological activity |
| biogeography | | study of the distribution of species |
| biosparite | | limestone including biogenic clasts |
| biostratigraphic (col | | a vertical sequence of fossils where the oldest lie at the bottom, the youngest at the top |
| biotic (succession) | | principle that fossils appear in a recognisable succession within each geological era |
| biotite | | hydrous potassium aluminium silicate mineral of the mica group |
| bioturbation | | disruption of sediment by burrowing or other organic activity |
| birefringence | | difference between the refractive indices of two minerals |
| birfurcation | | forking in two or more directions |
| bismuthinite | | bismuth sulphide |
| bituminous (coal) | | coal containing around 85% carbon |
| bivalve | | aquatic mollusc surrounded by two identical but reversed shells (mirror image) |
| bixbyite | | manganese iron oxide mineral |
| blackjack | | see sphalerite |
| blast | | prefix/suffix for large minerals formed during metamorphism |
| blastoid | | free swimming marine echinoderm |
| blastomylonitic | | texture of recrystalised rock that has been sheared and metamorphosed |
| blende | | see sphalerite |
| blocky (surface) | | lava surface consisting of polyhedral blocks |
| bodyplan | | distinctive arrangement of an organisms body parts, i.e. head, thorax, abdomen |
| boleite | | hydrated lead copper chloride mineral |
| bone-bed | | a bed rich in fossil bones |
| borax | | hydrated sodium borate |
| bornite | | copper iron sulphide |
| botryoidal | | globular rock formation resembling grapes |
| boudin | | effect in banded rocks where forces have stretched and broken the banding |
| boudinage | | a tectonic structure formed within a metamorphic environment |
| bouguer | | term relating to the measurement of gravitation force |
| boulangerite | | lead antimony sulphide mineral |
| boulder-clay | | see till |
| bouma | | sequence of sedimentary structures in turbidity current deposits |
| bourne | | river that only exists during periods of high rainfall |
| bournonite | | lead copper antimony sulphide |
| BP | | before present |
| brachiopod | | aquatic mollusc surrounded by two shells of uneven size or symmetry |
| braiding | | river possessing multiple interwoven channels |
| brash | | type of soil - mixture of clay and angular limestone fragments |
| brazilianite | | hydrous sodium aluminium phosphate mineral |
| brochantite | | hydrous copper sulphate mineral |
| bronzite | | magnesium iron silicate mineral |
| brookite | | titanium oxide mineral |
| brucite | | magnesium hydroxide mineral |
| bryozoa | | branch of small aquatic colonial animals |
| burgess (shale) | | Western Canadian location famous for its Cambrian fauna |
| butte | | isolated flat topped hill found in semi-arid regions |
| byne (disease) | | dissolution of calcareous rocks by acetic acid released from storage materials due to fluctuating humidity |
| byssus | | fibrous tuft with which a bivalve attaches itself to the seafloor, rocks etc |
