Lawrence, D.J.D., Vye, C.L. and Young, B. 2004. Durham Geodiversity Audit. Durham: Durham County Council
Glossary
| Alluvial | Sediments, which may be gravel, sand, silt or mud, which have been transported and deposited by rivers |
| Ammonoid | A subclass of molluscs with coiled shells belonging to the class Cephalopoda |
| Anticline | Arch-shaped fold of rocks, closing upwards |
| Argillaceous rocks | Sedimentary rocks composed of of very fine grain silt or clay-sized particles (<0.0625 mm), usually with a high content of clay minerals |
| Armour-Stone | Large stone block used in coastal defence and other engineering works |
| Aureole | Area surrounding an igneous intrusion affected by metamorphic changes |
| Basalt | A dark-coloured, fine-grained, usually extrusive, igneous rock composed of minerals rich in iron and magnesium and with a relatively low silica content |
| Batholith | A large body of intrusive igneous rock with no visible floor Biostrome A layered, sheet-like in situ accumulation of organisms Bituminous Rich in hydrocarbons or bitumen |
| Bivalve | A class of molluscs with paired shell valves |
| Blanket Bog | An extensive area of peat bog |
| Bouguer Anomaly | A gravity anomaly calculated after corrections for latitude, elevation and terrain. |
| Brachiopod | A phylum of solitary marine shelled invertebrates |
| Braided Rivers | A river consisting of a number of small channels separated by bars |
| Breccia | Coarse-grained clastic sedimentary rock consisting of angular fragments of pre-existing rocks |
| Breccio-conglomerate | A rock composed of both angular and rounded fragments of pre-existing rocks. It is intermediate in character between a breccia and a conglomerate |
| Brockram | A term used in NW England for breccias and conglomerates of Permo-Triassic age |
| Bryozoa | A phylum of small aquatic colonial animals |
| Calc-silicate | A group of minerals consisting of calcium silicates |
| Chert | A dense, microcrystalline form of silica which occurs as nodules or beds within parts of the Carboniferous succession of rocks |
| Chronostratigraphy | The standard hierarchical definition of geological time units |
| Cleavage | A property of rocks such as slate, whereby they can be split into thin sheets along aligned fractures or planes produced by the pressures that affected the rocks during severe earth movements |
| Columnar jointing | The crudely polygonal system of vertical joints formed in response to cooling of bodies of intrusive igneous rocks such as sills and dykes |
| Conglomerate | Coarse-grained clastic sedimentary rock composed of rounded or sub- rounded fragments of pre-existing rocks |
| Continental shelf | The gently sloping offshore zone, extending usually to about 200 metres depth |
| Crinoid | Or 'sea lillies' are marine animals composed of calcareous plates, belonging to the phylum Echinodermata |
| Cross-bedding | Internally inclined layers in a rock related to the original direction of current flow |
| Cupola | A dome-shaped offshoot rising from the top of a major igneous intrusion |
| Desiccation cracks | Or shrinkage cracks are polygonal cracks formed in a sediment as it dries out in a terrestrial environment |
| Displacement | The relative movement on either side of a fault plane |
| Doline | Or sink hole, is a steep-sided enclosed depression in a limestone region Dolomitic limestone A limestone containing a high concentration of the mineral dolomite Dolomitisation The process by which limestones are wholly or partially transformed into dolomite |
| Dry valley | A valley produced by running water but which is presently streamless |
| Dyke | Discordant, sheet-like bodies of intrusive igneous rock in a vertical, or near-vertical orientation |
| Evaporites | Sedimentary deposit of minerals formed by natural evaporation Fault A fracture in rocks along which some displacement has taken place Feldspar A group of rock-forming minerals consisting of silicates of aluminium, sodium, potassium, calcium and more rarely barium |
| Felsite | A general term used to denote fine-grained acid or feldspar-rich igneous rocks |
| Fissile | The tendency of a rock, such as a shale or slate, to split readily into thin sheets along closely spaced bedding or cleavage planes |
| Gangue | Generally valueless mineral or rock which accompanies an ore |
| Gastropod | Molluscs belonging to the class Gastropoda, usually with coiled shells |
| Gouge | Broken rock, often shale or clay, in a mineral vein or between fault planes |
| Graptolite | A group of extinct colonial marine organisms. Generally placed in the phylum Chordata, but sometimes regarded as Coelenterata. They consist of one or more branches or stipes in which individuals in the colony occur in rows |
| Greywackes | A sandstone containing a high proportion of silt, clay and rock fragments in addition to quartz grains |
| Hornfels | A fine-grained rock that has been partly or completely recrystallised by contact metamorphism |
| Hydrothermal | Processes involving hot ground waters. Includes the formation of mineral veins and the associated alteration of rocks in the formation of flat deposits |
| Inlier | An outcrop of older rocks surrounded by rocks of younger age |
| Joints | A fracture, or potential fracture, in a rock adjacent to which there has been no displacement |
| Lamprophyre | A group of intrusive igneous rocks characterised by abnormally high contents of silicate minerals such as biotite, hornblende and augite, with generally small amounts of feldspar |
| Lapilli-tuff | A compact rock composed of small pieces of lava or ash rounded during eruption |
| Lithified | Literally 'changed to stone'. Applied to loose sediment which has been consolidated to a solid rock |
| Lithology | The character of a rock expressed in terms of its mineral composition, structure, grain size and arrangement of its constituents |
| Magma | Molten rock |
| Magnetic anomaly | The value of the local magnetic field remaining after the subtraction of the dipole portion of the earth's field |
| Marl | An old term loosely applied to a variety of sediments which typically consist of intimate mixtures of clay and calcium carbonate |
| Metamorphism | Change in the mineralogy and structure of a rock as a result of the effects of heat and/or pressure |
| Millet seed grains | Smooth and conspicuously rounded sand grains which resemble millet seeds. Commonly with frosted surfaces resulting from wind action in desert environments. |
| Monocline | A one-limbed fold on either side of which the strata are horizontal or dip at only low angles |
| Mountain building | The complex series of geological processes which create mountains |
| Nunatak | An isolated mountain peak projecting from an ice sheet |
| Oolitic limestone | A limestone consisting predominantly of sub-spherical, sand-sized, concentric grains, or ooids, composed of calcite or dolomite |
| Ostracod | Small arthropods belonging to the subclass Ostracoda, having a twin shell |
| Outlier | A remnant of a younger rock surrounded by older strata Palaeomagnetic The magnetic characteristics of a rock formed in the geological past Pegmatite An igneous rock of especially coarse grain size |
| Phenocryst | Large crystals, usually of near perfect shape, embedded in a fine-grained matrix in igneous rocks |
| Phreatic | Volcanic eruptions generated by the interaction between hot magma and surface or ground water |
| Phyllites | A cleaved metamorphic rock characterised by a silky lustre due to minute flakes of white mica which are too small to be seen by the naked eye |
| Pisolitic limestone | A limestone consisting predominantly of sub-spherical, concentric grains larger than 2mm in diameter, or pisoliths, composed of calcite or dolomite |
| Porphyritic | The term applied to igneous rocks which contain isolated crystals, or phenocrysts, larger than those forming the main body of the rock |
| Pseudomorph | A secondary mineral, or a random aggregate of secondary minerals, which have replaced a pre-existing mineral, but have retained its shape |
| Radiometric dating | The method of determining the geological age by measuring the relative abundance of parent and daughter isotopes in rocks |
| Rendzina | A brown earth soil of humid or semi-arid grassland that has formed over calcareous parent material. |
| Ripple marks | Small scale ridges and troughs formed by the flow of water or wind over unconsolidated sandy or silty sediment. The fossilised equivalent of ripples found today on beaches and river sands |
| Rottenstone | Any highly decomposed but still coherent rock |
| Sedimentary rocks | Rocks formed by the accumulation of fragments from the wasting of previous rocks or organic materials, deposited as layers of sediment |
| Sill | A tabular igneous intrusion with concordant contacts with the surrounding wall rocks |
| Sink hole See doline | |
| Slate | A fine-grained metamorphic rock derived mainly from mudstone or shale, and which splits, or cleaves, readily into very thin sheets as result of the re-alignment of its constituent minerals during metamorphism |
| Statigraphy | The definition and description of the stratified rocks of the Earth's crust Streak The name given to the colour of the powder of a mineral or rock Stromatolite A laminated, mound-like structure, built up over long periods of time by successive layers or mats of algae or bacteria, which have trapped sedimentary material |
| Supergene | Alteration formed near the surface |
| Syncline | A concave-upwards fold with the youngest rocks in the centre |
| Syngenetic ore | A deposit formed simultaneously with the host rock and by similar or mineral deposit processes |
| Tailings | Fine-grained waste from mineral processing operations |
| Throw | The amount of displacement on a fault |
| Trilobite | Extinct marine arthropods characterised by having a segmented oval body divided into three segments |
| Tufa | A porous or cellular deposit of calcium carbonate deposited from lime- rich springs |
| Tuff | A rock formed of compacted volcanic fragments |
| Turbidity current | A dense sub-marine flow of mixed water and sediment, capable of very rapid movement |
| Unconformity | A substantial break in the succession of stratified sedimentary rocks following a period when no deposition was taking place |
| Volcaniclastic | A rock containing volcanic fragments in varying proportions |
| Xenolith | A foreign inclusion in an igneous rock |