| sabkha | | salt flats |
| sacchardoidal | | mineral grains resembling sugar |
| salband | | rock bordering a mineral vein |
| salic | | minerals rich in silicon and aluminium |
| saltation | | bouncing motion of wind or water borne particles |
| samarskite | | complex rare earth niobium tantalum oxide mineral |
| sandstone | | hardened consolidated sand |
| sanidine | | potassium aluminium silicate mineral |
| sapphire | | blue gemstone form of corundum |
| satin-spar | | see gypsum |
| saturated | | igneous rock containing a saturated solution of silicon dioxide mineral |
| scalar | | physical properties of minerals undependent of plane |
| scapolite | | complex silicate mineral |
| scarp | | steep slope inclined away from the direction of dip |
| scheelite | | calcium tungstate mineral |
| schist | | coarse grained metamorphic rock possessing a large proportion of mica crystals |
| schistosity | | texture of metamorphic rocks comprised of parallel or sub-parallel layers |
| sclerometer | | instrument for measuring relative hardness |
| scolecite | | hydrated calcium aluminium silicate mineral |
| scoria | | basaltic ejecta from a volcano |
| scorodite | | hydrated iron arsenate mineral |
| scree | | eroded angular material at the base of a slope |
| seamount | | underwater volcano |
| seat (earth) | | layer of fossilised soil found beneath a coal seam |
| secondary | | substance formed by the alteration of minerals |
| sectility | | minerals and rocks soft enough to be cut with a knife |
| sedimentary | | process where rock is laid down by sediments carried by the wind, rivers, ocean currents etc |
| seismogram | | see seismograph |
| seismograph | | instrument for measuring the magnitude of an earthquake |
| seismology | | the study of earthquakes |
| seismometer | | instrument for measuring the magnitude of an earthquake |
| selvage | | see salband |
| sepiolite | | hydrous magnesium silicate mineral |
| septa | | radial lines from the centre to the edge of a coral |
| septum | | a partition in a coral or shell structure |
| series | | subdivision of a group of rocks |
| serpentine | | hydrous magnesium iron silicate mineral |
| serpentinite | | metamorphic rock |
| sessile | | animal living in a burrow or attached to the seafloor |
| set | | collection of sedimentary layers |
| shale | | variety of mudstone displaying distinct layers |
| shard | | glass fragment from a pyroclastic eruption |
| shear | | sideways deformation of a rock through stress |
| shield | | stable continental basement rocks, usually Pre-Cambrian |
| siderite | | iron carbonate mineral |
| sill | | igneous material intruded into a fracture in "country" rocks |
| sillimanite | | aluminium silicate mineral |
| silt | | fine particles of sediment carried along by a river current |
| sinistral | | fault in which rocks are moved to the left |
| sink (hole) | | see pot-hole |
| siphon | | breathing tube of a mollusc |
| siphuncle | | air tube to the chambers of an ammonoid to control buoyancy |
| skarn | | metasomatic metamorphic rock |
| skutterudite | | cobalt arsenide mineral |
| slate | | metamorphic rock formed from recrystallised mudstone |
| slickenside | | lineations caused by strata slipping over one another |
| smithsonite | | zinc carbonate mineral |
| snout | | downstream end of a glacier |
| soapstone | | see talc |
| sodalite | | sodium aluminium silicate mineral chloride mineral |
| solfataras | | gas vent from an inactive volcano |
| solifluction | | slow downhill creep of soil and rock fragments |
| sparite | | coarse crystalline calcite mineral |
| species | | part of the taxonomic hierarchy |
| speleology | | the study of cave systems |
| sphalerite | | zinc iron sulphide mineral |
| spherulitic | | texture consisting of spherical grains of fibrous radiating crystals |
| spinel | | magnesium aluminium oxide mineral |
| spondumene | | lithium aluminium silicate mineral |
| sporopollenin | | outer skin of pollen and spores |
| spreite | | trace fossil displaying a web-like pattern within a U-shape |
| SSSI | | Site of Special Scientific Interest |
| stade | | single period of advancing ice shorter than a period of glaciation |
| stage | | a stratigraphic division of time |
| stalactite | | dripstone formation on the roof of caves |
| stalagmite | | dripstone formation on the floor of caves |
| staurolite | | hydrous iron magnesium aluminium silicate mineral |
| stephanite | | silver antimony sulphide mineral |
| stibiconite | | hydrous antimony oxide mineral |
| stibnite | | antimony sulphide mineral |
| stilbite | | hydrated sodium calcium aluminium silicate mineral |
| stipe | | branch of a graptolite colony |
| stock | | small intrusive pluton |
| stratigraphy | | study of rock successions |
| streak | | characteristic colour left on an unglazed porcelain plate when a mineral is rubbed against it |
| strewn-field | | area associated with a specific group of tectites or meteorites |
| strike | | horizontal plane at right angles to the dip |
| stromatolites | | intertidal mounds produced by the action of cyanobacteria |
| strombolian (eruption) | | slow regular emissions of gas and lava |
| strontianite | | strontium carbonate mineral |
| structure | | observable character of a rock from it's outcrop or from a hand specimen |
| subduction | | plane along which a plate is driven beneath it's neighbour by tectonic processes |
| sublimate | | a material that passes directly from a solid to a gaseous state |
| subsidence | | slow sinking of a land area |
| succession | | a sequence of strata |
| supratidal | | shoreline above the mean high water line |
| suture | | junction between septum and outer shell in an ammonoid |
| suture (zone) | | junction between two continents |
| swallow-holes | | see dene-holes |
| swash-bar | | ridge of sediment between runnels on a shoreline |
| S-waves | | seismic waves produced by shearing rock strata during an earthquake |
| syenite | | intrusive igneous rock |
| sylvanite | | silver gold telluride mineral |
| sylvite | | potassium chloride mineral |
| syncline | | a concave shaped fold |
| syntexis | | assimilation of rocks into a hot magma by melting |
| tabular | | composed of flat crystals |
| tailings | | see gangue |
| tailpiece | | see pygidium |
| talc | | hydrous magnesium silicate mineral |
| talus | | see scree |
| tantalite | | iron manganese niobium tantalum oxide mineral |
| tanzanite | | blue gemstone form of zoisite |
| tarbuttite | | hydrous zinc phosphate mineral |
| tarn | | small deep lake in a glaciated area |
| taxonomy | | classification of organisms |
| tectite | | a rock ejected from a volcano that displays re-entry fusion from being thrown into a sub orbital trajectory |
| tectonics | | the study of the movement of the plates forming the Earth's crust |
| telson | | anal segment of an arthropod |
| tenacity | | the resistance of a mineral to breaking |
| tennantite | | copper iron sulphide |
| tephrite | | extrusive igneous rock |
| terrace (river) | | gravel deposits left behind by a river that has receded |
| terrane | | constituent part of a continental crust |
| tertiary | | see cenozoic |
| tethys | | ancient sea formerly occupying the area now covered by the Mediterranean |
| tetrahedrite | | copper iron sulphide mineral |
| texture | | the combination of form, size and distribution of grains in a rock |
| theca | | cup-like structures on the stipe of a graptolite |
| thomsonite | | hydrated sodium calcium aluminium silicate mineral |
| thorianite | | thorium uranium oxide mineral |
| throw | | vertical displacement along a fault line |
| thulite | | red gemstone form of zoisite |
| tigers-eye | | silicon oxide mineral |
| till | | sediment deposited by a glacier |
| tillite | | consolidated till deposits |
| titanite | | calcium titanium silicate mineral |
| tonalite | | intrusive igneous rock |
| toolmarks | | in-filled striations caused by erosion through water or wind swept pebbles |
| topaz | | hydrous aluminium silicate mineral |
| topography | | geographic features of a landscape |
| topography (buried) | | fossil hills and valleys hidden by overlying deposits |
| tor | | granite boss exposed on a hillside - relict of a volcano |
| torbernite | | hydrated copper uranium phosphate mineral |
| torsion | | immature gastropod shell twisted 180º relative to the foot |
| tourmaline | | complex borosilicate minerals |
| trace (fossils) | | "fossilised structures associated with an organism such as burrows, footprints etc" |
| trachyte | | extrusive igneous rock |
| traction (load) | | see bedload |
| transgression (marine) | | invasion of land areas by the sea |
| trap | | general term for a dark lava flow such as basalt |
| trap (oil) | | fault or fold in which a reservoir of oil may be found |
| travertine | | carbonate mineral evaporite deposit around hot springs |
| tremolite | | hydrous calcium magnesium silicate mineral |
| trench | | deep valley in the ocean floor |
| trend | | direction of a stratum usually expressed as a compass bearing |
| triboluminescence | | emission of light by a mineral under friction |
| trichroism | | three different colours exhibited by a mineral depending on the plane viewed |
| tridymite | | silicon oxide mineral |
| trilobite | | extinct marine arthropod with three skeletal sections |
| trona | | hydrated sodium carbonate mineral |
| tsunami | | tidal wave caused by undersea earthquake activity |
| tufa | | a light carbonate evaporite rock |
| tuff | | consolidated fine grained pyroclastic ash |
| tumulus | | solid mound or dome-like structure on the surface of a lava flow |
| turbidite | | deposit formed through turbidity |
| turbidity | | movement of large volumes of deposited material under water |
| turquoise | | hydrated copper aluminium phosphate mineral |
| twin | | non symmetrical orientation of crystals of the same mineral |
