A glossary of geological terms used on this site
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Geologists are (in)famous for their long words and sometimes impenetrable terminology! This page may help you understand the site better. Where definitions refer you to the Geology Chart, please click HERE. The main Building Stone page will then open in a new window.
Ashlar: Building stone, rectangular, finely dressed (cut or sawn) with smooth external face and sides for close fitting
Bath Stone: Middle Jurassic limestone widely used in church windows and quoins
Bridport and Yeovil Sands: Geological formation extending from Dorset coast to Yeovil. See Geology chart
Bartonian: Geological time period. See Geology chart
Beer Stone: Local limestone once quarried in SE Devon. See Geology chart
Bembridge Limestone: Local limestone once quarried on Isle of Wight. See Geology chart
Bembridge Stone: Local limestone once quarried on Isle of Wight. See Geology chart
Binstead Stone: Local limestone once quarried on Isle of Wight. See Geology chart
Bioclast: Broken fossil shells, components of many limestones
Bivalve: Mollusc with two halves to its shell: clams, scallops, oysters, etc .
Blue Lias: Basal Jurassic Limestone, thin beds. Quarried in SW Dorset & Somerset. See Geology chart
Burr: Local limestone quarried on Isle of Purbeck. See Geology chart
Calcarenite: A limestone composed of sand-sized grains of calcium carbonate, usually shell debris.
Calcite: Calcium carbonate, defining component of all limestones.
Carboniferous: Geological time period. Rocks of this age not exposed in Dorset. Imported limestones used.
Chalk: Soft very fine-grained limestone. Geological formation widespread in S & SE England
Chert: Very hard rock composed of silica replacing sandstone or limestone in patches.
Cenomanian: Geological time period. See Geology chart
Chilmark: Area west of Salisbury where Portland Limestones quarried.
Clavellata: Species name of fossil bivalve. Geological formation name - See Geology chart
Concretions: Hard, dense, ovoid or spherical rock within a softer sedimentary rock layer.
Cornbrash: Middle Jurassic shelly oolitic limestone used as building stone. See Geology chart
Corallian: Upper Jurassic shelly limestone used as building stone. Geological Group - See Geology chart
Cretaceous: Geological time period. See Geology chart
Crinoid: Fossil marine animal related to starfish, also known as "Sea Lilies"
Current bedded: Sedimentary layers which were deposited inclined rather than horizontal; cross-bedding.
Cypris: A genus of ostracod (qv)
Dolomite: A mineral or rock largely composed of Calcium Magnesium Carbonate
Dressings: Building stones cut to a smooth face for windows, quoins, string courses
Echinoid: A Sea Urchin - a type of marine animal living on or within the sea bed
Eocene: Geological time period. See Geology chart
Featherbed: Very shelly local limestone once quarried on Isle of Wight. See Geology chart
Featherstone: Very shelly local limestone once quarried on Isle of Wight. See Geology chart
Ferroan: Containing iron minerals usually oxidised to an orange-brown colour; ferruginous
Ferruginous: Containing iron minerals usually oxidised to an orange-brown colour; ferroan
Flint: Very hard rock composed of silica replacing chalk in patches
Forest Marble: Middle Jurassic shelly limestones & sandstones used as building stone. See Geology chart
Freestone: Any rock which can be cut in any direction for building use
Fuller's Earth: Middle Jurassic clay with some limestones used as building stone. See Geology chart
Gastropod: A type of Mollusc, e.g.. Snail, which can live on land, in freshwater or in the sea
Glauconite: A green mineral formed from volcanic ash deposited in marine conditions
: Ham Hill Stone:Lower Jurassic coarse-grained bioclastic limestone, orange-brown. See Geology chart
Heathstone: A ferruginous sandstone used as a building stone. See Geology chart
Inferior Oolite: Middle Jurassic shelly limestone used as a building stone. See Geology chart
Ironstone: A sedimentary rock with a high iron mineral content; ferruginous. See Geology chart
Junction Bed: Lower Jurassic dense limestone, cream coloured. See Geology chart
Jurassic: Geological time period. See Geology chart
Kellaways: Middle Jurassic rock formation. See Geology chart
Knapped: Flint or chert which have been split and trimmed for use in building.
Laminations: Very thin layers within a sedimentary rock
Ledger slabs: Engraved slabs of rock used as gravestones, vertically or horizontally, inside a church
Limestone: A sedimentary rock containing more than 50% calcium carbonate
Lower Lias: A former division of the Jurassic. See Geology chart
Marble: In building use, any rock which can be polished for ornamental use. Not the geological meaning.
Marnhull Stone: Upper Jurassic oolitic limestone used as building stone. - See Geology chart
Micrite: Microcrystalline calcite (qv)
Middle Lias : A former division of the Jurassic. See Geology chart
Myophorella: Genus name of fossil bivalve Myophorella clavellata. Clavellata Formation - See Geology chart
Napped: Flint or chert which have been split and trimmed for use in building
New Vein: Local limestone quarried on Isle of Purbeck. See Geology chart
Non-Dorset: Here, sources of building stone imported for use in Dorset Buildings
Oolitic/Ooidal: Limestones (oolites) rich in spherical grains of calcium carbonate (ooids) formed in warm shallow seas
Osmington Oolite: Upper Jurassic oolitic limestone used as building stone. - See Geology chart
Ostracods: Small crustaceans with shell-like bodies (1-5mm) preserved in some building stones
Oxford Clay: Upper Jurassic rock Formation. See Geology chart
Paleocene: Geological time period. See Geology chart
Photomic.: Photomicrograph - photograph of a thin slice of rock viewed in a microscope
Plagioclase feldspar: Type of mineral common in sedimentary rocks derived by erosion of granites
Poikilitic: A rock texture in which small, randomly orientated, crystals are enclosed within larger crystals
Portland Stone: Upper Jurassic limestone. See Geology chart
Porosity: The percentage of space between the grains of a sedimentary rock
PPL: Plane Polarised Light - Microscopy term
Purbeck: Lower Cretaceous "rock Group". Geographical area in East Dorset. See Geology chart
Purbeck Marble: Lower Cretaceous gastropodal limestone, polished for decorative purposes. See Geology chart
Quarr: Very shelly local limestone once quarried on Isle of Wight. See Geology chart
Quartz: Silica mineral common in sedimentary rocks
Quoin: Architectural term: Corner stones of buildings
Render: Artificial coating applied to buildings
Ripple Marks: Minor undulations seen in sedimentary rocks deposited in shallow seas
Rubble: Dressed building stone (e.g. by hammer, guillotine) generally used between quoins, windows and ashlar courses
Sandstone: Sedimentary rock composed of mineral grains 0.062 to 2mm diameter, often quartz
Sarsen Stone: Hard quartzose non-marine sandstone. See Geology chart
Sedimentary: Rocks formed by the erosion of other rocks; by accumulation of organic matter; by evaporation of seawater
Shale: Sedimentary rock comprising clay which has been compressed by burial such that it splits horizontally
Slate: Metamorphic rock: originally clay, altered by pressure & heat such that it splits at an angle to the original
Sparite: Sparry calcite - calcium carbonate crystals large enough to be visible by the naked eye
Tertiary: Geological time period. See Geology chart
Todber Freestone: Upper Jurassic oolitic limestone used as building stone. See Geology chart
Trigonia: Genus name of a fossil bivalve
Unconformity: The contact where sedimentary rocks overlie older rocks with a time gap and often a different structure
Upper Greensand: Mid-Cretaceous glauconitic marine sandstone widely used for building. See Geology chart
Upper Lias: A former division of the Jurassic. See Geology chart
Veins: Thin mineral sheets, usually calcite, cross-cutting sedimentary rocks. Purbeck rock units - See Geology chart
Weald Clay: Lower Cretaceous rock Formation. See Geology chart
White Lias: Youngest Triassic limestone, pale, dense. See Geology chart
Wight Stone: Very shelly local limestone once quarried on Isle of Wight. See Geology chart
XPL: Cross Polarised Light - Microscopy term
Yellow Ledge Stone Band: Local stone in Kimmeridge Group. See Geology chart