Glossary

Acadian Orogeny See orogeny.

adit More-or-less horizontal tunnel to mine.

agate Variety of quartz with distinctive concentric colour banding.

alga (pl. algae) Primitive plant-like organism. Some may secrete calcium carbonate and algal mats may play a role in sediment accumulation in some environments. See stromatolite.

ammonite Extinct Mesozoic marine ammonoid mollusc (cephalopod), secreting a chambered shell of calcium carbonate, usually planispirally coiled (See goniatite).

anhydrite CaSO₄ White to grey, rock-forming evaporite mineral. anticline See fold.

argillaceous Describing silt to clay-grade sediments (grains less than 0.0625 mm in diameter).

arkose Sand-grade rock containing 25% or more feldspar.

aurichalcite (Zn,Cu)₅,(CO₃)₂,(OH)₆, Bright turquoise-blue mineral in radiating aggregates of thin pearly crystals. A secondary mineral in oxidized zones of zinc and copper bearing veins.

azurite Cu₃(CO₃),(OH), Deep azure blue mineral associated with the oxidized zone of copper deposits.

baryte/barytes BaSO₄ Baryte is a colourless to white mineral, crystals commonly tabular, noticeably heavy. A common gangue mineral. Barytes is the commercial product.

barytocalcite BaCa(CO₃)₂, Colourless to white or pale cream mineral.

basalt Dark, often almost black, fine-grained volcanic rock, low in silica (no quartz) and relatively rich in iron, magnesium and calcium.

belemnite Extinct mollusc (cephalopod). Internal skeleton consists of a solid calcium carbonate bullet-shaped 'guard' (part usually preserved), with chambered structure (phragmocone) in conical cavity at one end.

benthonic (benthic) Describing bottom-living organisms. bioclastic Limestone composed of shells or skeletal fragments.

biostratigraphy Use of fossils to date and correlate rock sequences.

biostrome Sheet-like accumulation of fossil shells or skeletons.

bioturbation The destruction of primary structures (i.e. bedding) in an unconsolidated rock unit by burrowing organisms; hence bioturbated.

biozone Fundamental unit of biostratigraphy.

bivalve Marine to fresh-water mollusc in which the plane of symmetry of the bi-valved calcium carbonate shell is in the plane of opening of the two valves (as in cockles and mussels).

blastoid Extinct Palaeozoic stalked echinoderm with a bud-like theca showing distinct pentameral symmetry.

bornite Cu₅FeS₂ (peacock ore) Reddish-brown to purplish-blue mineral, iridescent on tarnished surfaces; crystals often rough cubes.

brachiopod Solitary marine animal with bi-valved calcite shell. The plane of symmetry is perpendicular to the plane ofopening of the valves.

breccia Coarse clastic rock in which the clasts are angular. See also fault.

bryozoa Small colonial animal with a calcite skeleton consisting oflarge numbers of tiny tubular or box-like chambers. Colonial form very variable.

calcite CaCO Colourless or white mineral which is the main constituent of limestone. Crystals when formed (i.e. in veins) may be tabular or prismatic.

Caledonian Orogeny See orogeny.

carbonate rocks Limestones or dolostones (dolomites).

carnelian Reddish-white cryptocrystalline quartz.

chalcopyrite CuFeS₂ (copper pyrites) Brass-yellow mineral with an iridescent tarnish. Most common copper mineral. Crystals usually tetrahedra.

chalk Very fine-grained, white to pale grey, carbonate rock principally formed of coccolith ooze. Characteristic of the European Upper Cretaceous.

chamosite (berthierine) (Fe₅Al)(Si₃Al)O₁₀(OH)₈ Greenish-black mineral often found in sedimentary iron ores. Berthierine is the primary deposit which is converted to chamosite at moderate temperatures and pressures.

chert Nodules, lenses or impersistent bands of cryptocrystalline quartz, usually black, grey or red in colour, usually of diagenetic origin in sedimentary sequences.

chronostratigraphy Arrangement of rock sequences in terms of time.

cinnabar HgS Most common mineral of mercury, scarlet to brownish red.

clast Rock fragment; hence clastic rock. The principal clastic rocks are distinguished on grain size thus: conglomerate >2 mm > sandstone > 0.0625 mm > siltstones >0.004 mm> mudstone/shale.

Clast fabric (imbrication) may indicate direction ofwater flow where platy/tabular casts lean in the direction of the current.

cleavage A close-spaced, regular fracture or fabric imposed on strongly-folded beds and best developed in weaker, fine-grained rocks.

coccolith Minute calcium carbonate plate or disc, usually less than 0.02 mm in diameter, part of the covering of a microscopic marine, planktonic, unicellular alga. Coccolith ooze is a major component of chalk.

cone-in-cone Fabric of adjacent sets of vertically nested cones, each about 3 cm or more in diameter, caused by precipitation of CaCO₃ under pressure in a mud-grade rock.

concretion Spherical or ellipsoidal, resistant mass formed by local early cementation of the sediment.

conformable Sequence of rocks in apparently continuous succession.

conglomerate Coarse elastic rock in which the clasts are rounded. An intraformational conglomerate is one formed of locally derived clasts from a recently deposited source.

conodont A microscopic phosphatic, tooth-like fossil, part of the jaw apparatus of an extinct group of primitive vertebrates. Very useful in biostratigraphy.

coprolite Fossilised excreta.

coquina A (lenticular) bed consisting principally ofshells.

coral A polyp or polyps (anemone-like) with a basal skeleton ofcalcium carbonate. Corals may be solitary or colonial, the latter varying from flat, tabular masses to clusters of branching tubes.

crinoid (sea lilies; feather stars) Echinoderm with a plated cup bearing feeding arms, supported in sea lilies by a stalk. The disc-shaped ossicles or columnals of the stalk are a major constituent of Palaeozoic limestones, hence crinoidal limestone.

cross-stratification, cross bedding, cross-lamination Sedimentary structure in which the migration of the slip face of ripples, dunes or bars produces a series of inclined laminae (foresets) between sub-horizontal bedding surfaces. Different types are: planar, when the laminae are flat; trough, when the laminae are scoop-shaped; and hummocky, when individual sets of cross-beds cut across each other, leaving hummocky bounding surfaces.

cyclothem A sequence of beds, repeated again and again in vertical succession. Particularly notable in the Carboniferous.

dating, radiometric Rocks are dated by using the fixed rate of decay of parent isotopes of various radioactive elements to daughter products. The resulting age may be quoted with the parent isotope used, as in '¹⁴C yrs', etc.

diagenesis The changes that take place in the conversion of a sediment to a rock.

diamicton An unsorted sediment with a mixture oflarger clasts and a mud-grade matrix. Diamictite is the resulting rock.

dip The maximum angle of inclination of a planar surface, usually bedding. Measured in the vertical plane at right angles to the strike.

disconformity A break in the succession where the beds above and below are parallel.

disharmonic See fold.

dolomite CaMg (CO₃)₂ White, colourless, yellowish or brown mineral, in rhombic crystals with curved faces. Term also used for the characteristically brownish-yellow rock composed mainly of the mineral, but more correctly termed dolostone.

downthrow See throw.

drift Any superficial, unconsolidated sediments of the Quaternary.

drumlin Smooth, streamlined, oval mound oftill (boulder clay), usually in groups (drumlin field or swarm), formed beneath an advancing ice sheet. The long axis of the drumlin is parallel to the direction of advance.

dyke More or less vertical, cross-cutting intrusion.

echinoderms Marine invertebrates including echinoids, crinoids, blastoids, starfish and brittle stars. Characterized by a fundamental pentameral symmetry.

echinoid (sea urchin) Echinoderms with body enclosed in a globular or discoidal test. Symmetry either pentameral radial (regular echinoids) or pentameral bilateral (irregular, burrowing, echinoids).

epicontinental On continental crust, as in epicontinental sea.

epiplanktonic Organism living in plankton by attachment to other planktonic organisms or floating objects.

erratic Glacially transported rock derived from outside the local area.

esker Long, sinuous, steep-sided ridge consisting ofsands and gravels, formed either in an englacial tunnel or at the edge ofa retreating ice sheet.

eustatic World-wide change in sea level.

evaporite Rock or mineral formed by precipitation ofsalts from natural brines by evaporation.

facies Features ofa rock or rock sequence that reflect the environment of deposition.

fault A more or less planar fracture in a rock mass along which relative displacement of adjacent blocks has occurred. The hade is the inclination of the fault plane relative to the vertical. The face of the block above an inclined fault plane is the hanging wall, that below is the footwall. In most faults the direction of movement is known or assumed to be predominantly vertical. In a strike-slip or wrench fault, the direction of movement is predominantly horizontal. A thrust fault has a subhorizontal plane ofdisplacement. Fractured rock on the fault plane caused by movement between adjacent blocks is a fault breccia.

feldspars Importantgroup of rock-forming silicate minerals, common in igneous rocks and usually broken down quickly on weathering. Hence feldspathic.

fireclay See seatearth.

flat A lenticular zone of mineralization parallel to bedding.

flint A variety of cryptocrystalline quartz commonly present as grey or grey/black nodules and bands in chalk. It probably formed as a gel from organic silica (sponge spicules), and may fill or replace fossil tests, shells and burrows.

fluorite CaF₂ Colourless to translucent yellow, green, blue or purple, more rarely red or black mineral commonly crystallizing in cubes. Fluorspar is the commercial product.

flute cast (flute mark) See sole structure.

fold A bend in bedded rocks or any planar rock mass. An anticline is arched upwards with older rocks in the core. A syncline is bent downwards with younger rocks in the core. An isoclinal fold has subparallel fold limbs. The dip of the fold axis is the plunge of the fold. Folds are disharmonic when they change shape and/or size when traced into adjacent beds.

footwall See fault.

foraminifera Microscopic single-celled organism with a chambered, usually calcium carbonate, test.

foresets See cross-stratification.

galena PbS Lead-grey mineral crystallizing in cubes and octahedra.

gangue Bulk mineral in veins, formerly of no commercial importance, with which ore minerals are associated (i.e. quartz, fluorite, baryte). ganister See seatearth.

garnet Silicate mineral ofvariable composition, often deep reddish-brown in colour, found in igneous and metamorphic rocks.

gastropod Mollusc with a usually helically coiled calcium carbonate shell (snail) or naked (slug).

gelifluctate Rock material derived from flow ofwater-saturated sheets of rock debris over perennially frozen ground (cold climate variety of solifluction).

glaciofluvial Sediments or landforms produced by meltwater from a glacier.

glauconite Silicate clay mineral, characteristically green, formed in some marine sediments.

gneiss Coarse-grained, banded rock formed under high-grade metamorphic conditions.

goniatite Palaeozoic ammonoid. Goniatites are the direct ancestors of the ammonites.

graben A linear tract of country, lowered between two bounding faults. A half-graben is fault-bounded on one side only.

graptolite Extinct group of marine, pelagic, colonial organisms with an organic skeleton.

gypsum CaSO₄.2H₂O Evaporite mineral, usually white, as tabular crystals or massive. A transparent variety (selenite) may be precipitated within sediments under some conditions.

gyttja Rapidly accumulated organic-rich muddy deposit.

hade See fault.

half-graben See graben.

halite (rock salt) NaCl Common salt, an evaporite mineral, usually white; crystals usually cubes.

hanging wall See fault.

hemimorphite (calamine) Zn 4(Si₂O₇) (OH)2.H₂O White, grey, green-brown or pale blue ore ofzinc, small tabular crystals but normally radial or earthy masses.

hummocky cross-stratification See cross-stratification.

igneous Rocks crystallized or solidified from a molten state.

inlier Area ofolder rocks surrounded by younger rocks.

intermontane basin Sedimentary basin being infilled from erosion of surrounding mountains.

interstadial A period of increased warmth or retreating ice between stadials.

intraclast Carbonate fragment derived from the erosion 01 a nearby sediment and redeposited within the same area.

joint Fracture in rock, usually occurring in more or less regularly spaced sets, along which little or no movement can be detected.

kame Steep-sided mound of bedded glaciofluvial sand and gravel associated with stagnant ice. A kame terrace is a continuous linear feature formed between an ice mass and a valley wall. Subsequent ice melt may result in signs of marginal slumping.

kettle hole Depression in glacial drift, possibly containing a lake, left by the melting of an included mass ofice.

lacustrine Sediments or processes associated with lakes.

laterite Crust of mainly hydrated iron and aluminium silicates produced by the weathering of certain rocks in tropical, humid conditions.

limonite FeO (OH).nH₂O Yellowish-brown earthy mineral derived from the weathering of iron minerals in rocks.

lithology Physical features ofa rock. Hence lithostratigraphy, the stratigraphic ordering ofdifferent rock types.

loess Unconsolidated, wind-deposited, mainly silt-grade sediment.

Ma Abbreviation for 'million years'.

magma A hot, liquid or semi-liquid melt within the Earth's crust; the source for all igneous rocks and processes.

malachite Cu₂CO₃(OH)₂ Bright green mineral usually found in banded spheroidal aggregates. A common secondary mineral in oxidized zone of copper deposits.

marcasite FeS₂ Pale bronze-yellow mineral, often occurring in spherical masses of radiating crystals in chalk.

marl A calcareous clay with 35–65% soft calcium carbonate.

meltwater channel Channel cut by the action of meltwater from a glacier or snow. Usually unrelated to the present drainage pattern.

mesothem An approximately 5 Ma cycle of eustatic rise and fall of sea level. In the Carboniferous, many cyclothems may form sequentially within a mesothem.

metamorphic Rock formed by the alteration ofa pre-existing rock by changes in temperature and/or pressure.

mica One ofa group of silicate minerals characterized by a platy habit.

microfossil Any fossil too small to be studied without a microscope. mineral veins See veins.

mollusc One of a very diverse invertebrate group including the bivalves, gastropods, cephalopods (ammonites, goniatites, belemnites and orthocones) and scaphopods.

moraine An unsorted deposit of rock debris associated with the actions of a glacier.

nannofossil Extremely small fossil derived from nannoplankton, generally less than 0.05 mm in size, for example a coccolith.

non-sequence Any (usually) minor break in the rock sequence.

nunatak Rocky summit standing above a surrounding ice sheet during glaciation.

oncolite Spherical or sub-spherical particle, up to 5o mm in diameter, formed by the action ofalgae in trapping sediment on the surface ofa mobile grain.

onlap See overlap.

ooid (oolith) Spherical to sub-spherical particle, less than 2 mm in diameter, formed by the concentric deposition of rings of (usually) calcium carbonate around a mobile grain.

oolite Rock formed largely of ooids. Characteristic of high-energy, shallow-water environments.

orogeny Process of mountain building by the lateral compression of thick rock sequences. The Caledonian Orogenic Cycle refers to a series of orogenic events in the Lower Palaeozoic of which the Acadian Orogeny (Lower Devonian) was the last. The Variscan Orogeny, whose main effects are seen in southwest England and Central Europe, spanned the late Devonian to late Carboniferous.

orthocone Extinct cephalopod mollusc with a straight, tapering, chambered shell.

outlier Area of younger rocks surrounded by older rocks.

overflow channel, spillway Channel carved by the overflow from an ice-dammed lake. Usually unrelated to the present drainage pattern.

overlap Relationship where successive beds of rock deposited by a transgression extend further than the one below, to rest in turn on (onlap) the surface of unconformity.

overstep Relationship where a bed deposited by a transgression rests on the eroded ends of several beds below the plane of unconformity.

paraglacial Subaerial processes acting on sediments and landforms produced by glaciation.

pelagic Organisms living in the body of the water, either floating (planktonic) or swimming (nektonic).

piedmont Tract of country at the foot of a mountain range.

pisolith Spherical to sub-spherical inorganic carbonate particle characterized by internal concentric lamination, usually several mm in diameter.

plate A part of the Earth's rigid outer shell (lithosphere), internally relatively free of earthquakes and volcanic activity but bounded by more or less continuous zones of earthquakes and volcanoes where the plates move against each other. Plate tectonics describes the processes and effects of plate motions and interactions.

plunge See fold.

pluton A large igneous intrusion.

progradation The outward extension of a sedimentary deposit, such as a delta building out from a shoreline.

pyrite FeS₂ (fools gold) Common pale brass-yellow mineral, often crystallizing in cubes.

pyromorphite Pb₅(PO₄)₃Cl Green, yellow or brown mineral, often with hollow prismatic or barrel-shaped crystals. A secondary mineral occurring in the oxidized zones of lead deposits.

quartz SiO₂ Very common mineral, usually transparent or white but may be variously coloured. Occurs in many igneous and metamorphic rocks, is the main constituent of sandstones and siltstones and a common gangue mineral in veins.

regression Withdrawal of the sea from the land area due to a relative fall in sea level.

rock-salt See halite.

scaphopod Marine mollusc with a tusk-shaped hollow shell.

seatearth A fossil soil with root traces found immediately below a coal seam. A fireclay is a pure clay seatearth, whilst a ganister is a pure quartz sand seatearth.

selenite See gypsum.

septarian Nodules or concretions with a series ofinternal mineral-filled (usually calcite) cracks.

siderite FeCO₃ Grey to grey-brown mineral widespread in certain sedimentary rocks, particularly sedimentary ironstone deposits and Coal Measures sequences.

siliciclastic Clastic rocks formed predominantly of quartz, other silicate minerals and rock fragments.

sill A tabular igneous intrusion, mainly concordant with bedding, although it may cut across beds from one level to another.

slickensides A lineation on a fault or bedding plane caused by the relative movement of rock masses on either side. The surface is often coated by fibrous crystals, usually of quartz or calcite, aligned in the direction of movement.

smithsonite (calamine) ZnCO₃ Grey, brown or greyish-white mineral, usually occurring as spherical aggregations or stalactitic masses.

sole structure Sedimentary structure cut into an underlying mudstone by a turbidity current and infilled by the overlying turbidite bed. Preserved as a cast on the base of the turbidite. Flute cast (mark): ovoid scoop-shaped structure caused by turbulent water flow, preserved as a lobe on the base of the turbidite.

solifluction Downhill movement ofsurface layer ofunconsolidated weathered material when saturated by water.

sphalerite (blende) ZnS Commonly a brown or black mineral with a resinous lustre and variable form. Most common ore for zinc. spillway General term for meltwater or overflow channels.

sponge Primitive invertebrates with an often asymmetrical body supported by spongin and/or siliceous or calcareous spicules. S.S.S.I. Site of Special Scientific Interest.

stadial A period ofincreased cold or advancing ice.

strike Intersection ofa bedding plane, or other planar surface, with the horizontal.

strike-slip See fault.

stromatolite A carbonate rock with a fine horizontal, domal or columnar banding, reflecting the control of deposition by an algal mat or microbial community living on the surface of the sediment.

strontionite SiCO₃ White to pale green, grey or pale yellow mineral, usually with prismatic or needle-like crystals.

stylolite An irregular, suture-like contact, most common in limestones, produced by solution of the rock under high pressure.

subduction The process whereby oceanic crust descends into the interior of the Earth beneath oceanic or continental crust at a convergent plate margin.

syncline See fold.

tectonic Caused by deformation of rock masses, as in mountain-building episodes.

tholeiitic basalt A type of basalt oversaturated in silica, so that small amounts of quartz are present.

throw Description of vertical component of movement on a fault plane. Downthrow emphasises the relative downward displacement ofa block on one side of the fault, upthrow (less commonly used) emphasizes the relative upward displacement ofa block.

thrust See fault.

till (boulder clay) Collective term for the group of unsorted sediments laid down by direct action of ice.

trace fossil A structure, such as a burrow or a grazing trail, resulting from the activity of an animal.

transgression An advance of the sea over the land, caused by a relative rise in sea level.

tufa Rock formed by the deposition of calcium carbonate (more rarely silica) as a sometime porous and/or banded mass around saline springs, or associated with stalactites and stalagmites.

turbidite Rock deposited from a turbidity current, a fast-flowing current charged with a high sediment load, initiated by the disturbance of soft sediment on a slope. A turbidite is poorly sorted but may show grading and sole structures on its base.

unconformity Surface of contact between two groups of rocks resulting from the tilting or folding and erosion of the lower group (often in an orogenic event) before the deposition of the upper group.

Variscan Orogeny See orogeny.

vein A fracture, usually sub-vertical, which is mineralized, often with quartz or calcite. A mineral vein implies the presence of ore minerals.

witherite BaCO₃ A white or grey mineral, crystals six-sided prisms and pyramids. Notably heavy.

Yoredale Name applied to repeat cycles oflimes tone-shalesandstone(-seatearth-coal) (cyclothems) in the Carboniferous (Dinantian, early Namurian), derived from the old name for Wensleydale, where they are typically developed.