| obduction | | process where dense oceanic crust is thrown onto continental sediments instead of being subducted back into |
| obsidian | | black shiny glassy rock of volcanic origin |
| ocellar | | texture of metamorphic rocks comprising radiating groups of platy minerals |
| ochre | | earthy mass of minute yellow/brown crystals used as a pigment |
| old-red-sandstone | | desert sandstone deposited in the British Isles during the Devonian |
| oligoclase | | sodium calcium aluminium silicate mineral |
| olivenite | | hydrous copper arsenate mineral |
| olivine | | iron/magnesium rich silicate mineral |
| olivine | | magnesium iron silicate mineral |
| omphacite | | calcium magnesium iron aluminium silicate mineral |
| ontogeny | | development of an organism where the adult form is markedly different to its juvenile form |
| onyx | | silicon oxide mineral |
| ooids | | round grains within a limestone |
| oölite | | rock composed of spherical grains, each less than 2mm in diameter |
| ooliths | | see ooids |
| ooze | | mud on the ocean floor containing calcareous or siliceous microfossils |
| opal | | hydrous silicon oxide mineral |
| opencast | | method of extracting ores by the digging of an open quarry rather than by a pit with underground tunnels |
| opercula | | lid in some molluscs that covers the aperture |
| ophicalcite | | consolidated fragments from landslides and tectonic movements |
| ophiolite | | mafic or ultramafic rocks formed from extrusion of mantle material from the ocean floor |
| ophitic | | texture of mafic igneous rocks composed of euhedral plagioclase crystals cemented by anhedral crystals of pyroxene |
| orbicular | | rock structure containing round inclusions made up of layered minerals of different habit and colour |
| order | | part of the taxonomic hierarchy |
| ordnance-datum | | mean sea level at Newquay, Cornwall from which all British contour heights are measured |
| ordnance-survey | | organisation responsible for producing topographical maps of the British Isles |
| ore | | rock containing an economically recoverable metal |
| organogenetic | | of organic origin |
| orogenesis | | deformation of the Earth's crust by tectonic processes leading to the formation of mountain ranges |
| orogenic (belt) | | range of mountains produced by tectonic movements |
| orpiment | | arsenic sulphide mineral |
| orthoclase | | potassium aluminium silicate mineral |
| ossicle | | calcareous segments that form the skeleton of a crinoid |
| ostracod | | tiny crustacean enclosed by two oval shells |
| otoliths | | ear bones of fishes and aquatic mammals |
| outcrop | | exposure of underlying rocks at the surface |
| outlier | | area of younger rocks surrounded by older ones |
| ox-bow | | a river meander that has been cut off from the main flow by sedimentary deposition |
| pahoehoe | | smooth lava with a ropey texture |
| palaeobiogeography | | study of the geographical distribution of animals from fossil evidence |
| palaeobotany | | study of fossil plants |
| palaeoecology | | study of ancient environments |
| palaeogene | | oldest periods of the Tertiary era |
| palaeolithic | | old stone age - period prior to 8000BC |
| palaeomagnetism | | orientation of the Earth's magnetic field recorded in the alignment of rocks |
| palaeontology | | the study of fossils |
| palaeosome | | original rock type before anatexis |
| palaeozoic | | era covering the period from 570 to 230 million years ago |
| pallial | | line on the inside of a bivalve shell marking the attachment point of the muscle folds |
| pan | | thin layers/nodules of iron oxide mineral formed by precipitation out of the stratas above |
| pangaea | | single "supercontinent" that existed prior to the Jurassic |
| paragenesis | | order of formation of minerals in a rock |
| paramorphism | | the changes in a substance's physical state but without change to it's crystalline structure |
| pargasite | | complex silicate mineral |
| pavement | | horizontal outcrop of limestone where all strata above have been eroded away |
| peat | | immature coal formed by decaying plants in a waterlogged anaerobic environment |
| pectolite | | hydrous calcium silicate mineral |
| pedicle | | fleshy stalk that attaches a brachiapod to the sea floor |
| pegmatite | | coarse grained mineral vein containing large crystals |
| peizo-electric | | minerals that produce electrical charges when subjected to stress |
| pelagic (1) | | sediment formed at depth in the oceans |
| pelagic (2) | | animals that live above the sea floor, opposite of benthic |
| pelites | | generic term for mudrocks and shales |
| pelitic | | sedimentary rock with grains of less than 1/16mm in diameter |
| pellet | | oval shaped fossil excrement often a constituent of limestone |
| peneplain | | flat plain produced by erosion |
| penninite | | hydrous magnesium iron aluminium silicate mineral |
| pennsylvanian | | US equivalent of the Upper Carboniferous |
| pentlandite | | iron nickel sulphide |
| peridot | | green gemstone form of olivine |
| peridotite | | dense coarse grained crystalline rock making up much of the mantle |
| periglacial | | processes acting at the margin of a glacier |
| period | | a major time unit within an era |
| perlitic | | texture of igneous rocks containing small subspherical glassy masses |
| permafrost | | subsoil that remains frozen all year round |
| permeability | | ability of liquids to pass through a solid |
| perovskite | | calcium titanium oxide mineral |
| persilicic | | rock with a high silica content |
| perthite | | deposition from solution of feldspar containing sodium or potassium |
| perthite | | potassium aluminium/sodium aluminium silicate mineral |
| perthitic | | layered texture of alkali feldspars |
| petalite | | lithium aluminium silicate mineral |
| petrography | | see petrology |
| petrology | | study of rocks and their formation |
| phanerozoic | | unit of geological time comprising the palaeozoic, mesozoic and cenozoic eras |
| phenakite | | beryllium silicate mineral |
| phenocryst | | crystal inclusion of large size compared to the crystal size of the surrounding rock |
| phenotype | | sum of all the characteristics of an organism |
| phillipsite | | hydrated potassium sodium aluminium silicate mineral |
| phlogopite | | hydrous potassium aluminium silicate mineral |
| phonolite | | extrusive igneous rock |
| phosgenite | | lead carbonate chloride mineral |
| phosphophyllite | | hydrated zinc iron manganese phosphate mineral |
| phosphorescence | | photoluminescence that continues after exposure to a radiation source has ceased |
| phosphorite | | organogenetic sedimentary rock |
| photic zone | | upper layers of a body of water where sunlight can penetrate |
| phragmacone | | the shell of a cephalopod |
| phyllite | | fine grained metamorphic rock made up of clay particles that have recrystallised through exposure to high t |
| phylum | | part of the taxonomic hierarchy |
| phyric | | texture of an igneous rock containing phenocrysts set in a fine matrix |
| piemontite | | hydrous calcium aluminium manganese silicate mineral |
| pillow (lava) | | physical form of lava that has undergone rapid cooling under water |
| pilotaxitic | | volcanic rocks made up of feltlike mats of minute crystals |
| pipe | | volcanic tubular structure through which lava travels |
| pisolite | | rock composed of spherical grains of greater than 2mm in diameter |
| pitchblende | | see uraninite |
| placer | | alluvial or glacial deposit of heavy minerals |
| plagioclase | | lamellar twinned mineral of the feldspar group |
| plate | | one of a number of sections making up the Earth's crust |
| plateau | | flat raised landmass |
| playa | | temporary lake formed in a desert |
| pleistocene | | oldest period in the Quaternary era |
| pleura | | lateral segments on the carapace of a trilobite |
| plucking | | process where rocks and boulders are taken up by the base of a glacier |
| plunge | | angle from the horizontal and direction from North of a fold |
| pluton | | underground coarse grained igneous body |
| podsol | | poor grey soil found in heavily forested areas in temperate zones |
| poikilitic | | texture of igneous rocks composed of crystal concretions |
| poikiloblastic | | texture of metamorphic rocks composed of crystal concretions |
| polariser | | lower filter in a polarising microscope |
| polybasite | | silver copper antimony sulphide mineral |
| polymerisation | | a large molecule made up of a chain of smaller molecules |
| polyp | | sedentary, non mobile, coral |
| polysynthetic | | pseudosymmetry caused by multiple twinning of crystals |
| porphyritic | | see phyric |
| porphyroblast | | phenocrysts set in a finer groundmass of a metamorphic rock |
| posterior | | rear end of an animal |
| potholes | | holes eroded by the action of water along faults and cracks in limestone |
| prasinite | | metamorphic rock - a type of chlorite schist |
| prehnite | | hydrous calcium aluminium silicate mineral |
| priscoan | | era covering the period from 4500 to 4000 million years ago |
| prodelta | | the furthest part of a delta from the shoreline |
| proglacial | | zone behind the icefront of a glacier |
| prograde | | progressive increases in temperature or pressure |
| prokaryote | | single celled animal with no nucleus |
| proterozoic | | era covering the period 2500 to 570 million years ago |
| protista | | see protozoa |
| protozoa | | animal phylum containing single celled micro-organisms |
| protrusion | | solid or semisolid magmatic mass pushed up by volcanic pressure |
| proustite | | silver arsenic sulphide |
| province | | large area displaying similar geological features |
| proximal (1) | | sediments laid down closest to their point of origin |
| proximal (2) | | along the axis of a body |
| pseudomorphism | | the ability of one mineral to replace another but without change to the overall crystalline habit |
| pseudotachylite | | fine grained or glassy rock formed by frictional heat along a fault plane |
| psilomelane | | hydrous barium manganese oxide mineral |
| puddingstone | | conglomerate rock |
| pumice | | light brown or grey volcanic rock filled with vesicles |
| purpurite | | manganese iron phosphate mineral |
| puy | | a steep sided tower of volcanic rock |
| P-waves | | compression waves created by a seismic disturbance |
| pycnometer | | instrument for measuring the specific gravity of a rock |
| pygidium | | posterior portion of a trilobite |
| pyrargyrite | | silver antimony sulphide mineral |
| pyrite | | iron sulphide |
| pyroclastic | | explosive and violent volcanic eruption |
| pyroelectric | | minerals that produce electricity when heated |
| pyrolusite | | manganese oxide mineral |
| pyromorphite | | lead phosphate chloride mineral |
| pyrope | | magnesium aluminium silicate mineral |
| pyrophyllite | | hydrous aluminium silicate mineral |
| pyroxene | | iron/magnesium/silicate mineral found in igneous rocks |
| pyroxenite | | intrusive igneous rock |
| pyrrhotite | | iron sulphide |
| rabsodome | | group of graptolites forming a colony |
| radioactivity | | spontaneous disintegration of an atomic nucleus during emission of radioactive particles or electromagnetic |
| radiolaria | | microscopic animal remains |
| radiolarites | | organogenetic sedimentary rock similar to flint |
| radula | | hard ridged surface used by a mollusc as teeth |
| rag | | hard limestone found in Kent |
| raised-beach | | ancient shore-line left behind by regression |
| realgar | | arsenic sulphide |
| redbeds | | rocks rich in iron oxide mineral |
| reef | | marine ridge built up from the skeletons of colonial animals such as corals |
| regolith | | unconsolidated surface layers, i.e. soils |
| regression (marine) | | major retreat of the sea |
| relicts | | rock left unchanged following alteration by metamorphosis |
| replacement | | substitution of one mineral for another |
| residual | | mineral left after parent rock has been disintegrated by a process |
| retrograde | | progressive decreases in temperature or pressure |
| reworking | | erosion and redistribution of a sediment |
| rheic | | ocean that once separated north-west europe from the rest of the european landmass during the Silurian era |
| rhizome | | horizontal underground stem from which roots diverge |
| rhodochrosite | | manganese carbonate mineral |
| rhodonite | | manganese iron magnesium silicate mineral |
| rhyolite | | fine grained or glassy volcanic rock |
| ribs | | ridge on the outside of an ammonite shell |
| richter (scale) | | measurement of the magnitude of an earthquake in released energy |
| richterite | | hydrous sodium magnesium silicate mineral |
| riebeckite | | hydrous sodium iron magnesium silicate mineral |
| rift (valley) | | see graben |
| RIGS | | Regionally Important Geological Site |
| ripple-bed | | current ripples preserved in sediment |
| roche-moutonee | | sheep shaped rock scoured by glacial action |
| rock-flour | | fine particles produced by glacial action |
| romanechite | | hydrous barium manganese oxide mineral |
| rondingite | | metasomatic metamorphic rock |
| rosasite | | hydrous copper zinc carbonate mineral |
| rose (quartz) | | silicon oxide mineral |
| rostrum | | the internal skeleton of a belemnite |
| rotten-flint | | hollow spherical flint nodule containing sponge spicules |
| ruby | | red gemstone form of corundum |
| runnel | | shallow depressions formed by wave action moving sediment up a beach |
| rutile | | titanium oxide mineral |
