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Lithotype : Specific types of rock classified according to the standards of lithology.

Loess : A fine, silty, pale yellow or buff-coloured, windblown (eolian) type of unconsolidated deposit.

Lithotype : Specific types of rock classified according to the standards of lithology.

Lithology : A description of the physical characteristics of a rock unit visible at outcrop, in hand or core samples or with low magnification microscopy, such as colour, texture, grain size, or composition.

Lithification : The process by which sediments compact under pressure, expel connate fluids, and gradually become solid rock.

Lithic fragment : Also simply called a lithic.

A sand-sized grain that is made up of smaller than sand-sized grains, e.g. a shale fragment or basalt fragment in a sandstone.

 Liquefaction : Soil liquefaction describes the behavior of soils that, when loaded, suddenly suffer a transition from a solid state to a liquefied state, or having the consistency of a heavy liquid.

Limestone : A sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO₃).

Leucocratic : A term used to denote a light colour in igneous rocks, due to a high content of felsic minerals and a correspondingly small amount of dark, heavy silicates.

Lava : Molten rock expelled by a volcano during an eruption.

Lamprophyre : Igneous rocks usually occurring as dykes intimately related to larger intrusive bodies; characterised by abnormally high contents of coloured silicates, such as biotite, hornblende and augite, and a correspondingly small amount of feldspar, some being feldspar-free.

Lacuna : A time-stratigraphic unit representing the gap in the stratigraphic record. Specifically the missing interval at an unconformity, representing the interpreted space-time value of both hiatus (period of non-deposition), and degradation vacuity (period of erosion).

Kyanite: A silicate of aluminium which crystallises in the triclinic system. It usually occurs as long-bladed crystals, blue in colour, in metamorphic rocks.

Kink band : An asymmetric, linear zone of deformation characterised by a tight curled, twisted, or bended rock band. Kink bands may also occur as conjugated sets.

Kink : A tight curl, twist, or bend in a rock band. See also folding and buckling.

Kettle : A fluvioglacial landform occurring as the result of blocks of ice calving from the front of a receding glacier and becoming partially to wholly buried by glacial outwash.

Karst : A distinct type of landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Karst topography is usually characterised by closed depressions or sinkholes, caves and underground drainage.

Kaolinite : A finely crystalline form of hydrated aluminium silicate occurring as minute monoclinic flaky crystals with a perfect basal cleavage, resulting mainly from the alteration of feldspars under conditions of hydrothermal or pneumatolytic metamorphism.

Kame : An irregularly shaped hill or mound composed of sand, gravel and till that accumulates in a depression on a retreating glacier and is then deposited on the land surface with further melting of the glacier.

Ka : A non-standard but widely used abbreviation for one thousand (1,000) years, using the metric prefix K (for “Kilo”) to indicate a quantity of one thousand. When not otherwise qualified, it usually indicates 1,000 years Before Present (or 1,000 years ago).

Jurassic : A major unit of the geologic timescale that extended from about 199.6 ± 0.6 Ma (million years ago) to 145.4 ± 4.0 Ma, between the end of the Triassic and the beginning of the Cretaceous.

Joint : A discrete discontinuity surface without evidence of displacement. See also diaclase or bedding.

Isotope : different forms of an element each having different atomic mass (mass number).

Isomorphic : Two crystals that have similar shapes and sizes, usually through the angles.

Island arc :A chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.

Intrusion : body of igneous rock that has crystallized from molten magma below the surface of the Earth.

Interbedded : beds (layers) of rock lying between or alternating with beds of a different kind of rock.

Indurated : Made hard (by heat or compaction).

Ilmenite : An oxide of iron and titanium, crystallising in the trigonal system; a widespread accessory mineral in igneous rocks, especially those of basic composition.

Ignimbrite : Fine-grained to aphanitic, buff to dark brown compact rock with parallel streaks or lenticles of black glass, produced by violently explosive volcanoes.

Igneous rock : A type of rock formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.

Idiomorphic : Bounded by the crystal faces peculiar to the species, used of minerals. Synonymous with euhedral.

Ichnology : A branch of biology that deals with traces of organismal behavior.

Hypersaline : Having a saltiness or dissolved salt content greater than that of seawater.

Hydrothermal vent: A fissure in a planet’s surface from which geothermally heated water emerges.

Hydrothermal: Pertaining to the actions or products of heated water.

Hot spring : A natural spring resulting from the emergence of geothermally heated groundwater from beneath the Earth’s crust.

Horst : A raised fault block bounded by normal faults.

Hornfels : A hard, compact, fine-textured contact-altered argillaceous rock that breaks into splintery fragments.

Hornblende : An important rock-forming mineral of complex composition, essentially a silicate of calcium, magnesium and iron, with smaller amounts of potash, soda and hydroxyl. Hornblende crystallises in the monoclinic system and occurs as black crystals or grains in many different types of igneous and metamorphic rocks, including hornblende-granite, syenite, diorite, andesite, hornblende-schist, and amphibole.

Holocrystalline : Having the properties of those igneous rocks in which all of the components are crystalline; glass is absent. Contrast hemicrystalline.

Hinge line : A line joining the points of maximum curvature along the hinge of a fold.

Hinge :The zone of maximum curvature of a fold.

Hemicrystalline : Having the properties of certain rocks of igneous origin which contain some interstitial glass in addition to crystalline minerals. Contrast holocrystalline.

Half-life : The time it takes for a given amount of a radioactive isotope to be reduced by one-half.

Habit : See crystal habit.

Grus : Freshly eroded, angular grains of quartz and feldspar derived from a granitoid.

Greenstone : An omnibus term lacking precision and applied indiscriminately to basic and intermediate igneous rocks of Lower Paleozoic age in which much chlorite has been produced at the expense of the original coloured minerals, staining the rocks green.

Graywacke : A variety of sandstone generally characterized by its hardness, dark colour, and poorly sorted, angular grains of quartz, feldspar, and small rock fragments (lithic fragments) set in a compact, clay-fine matrix. Also spelled greywacke.

Granodiorite : An intrusive, felsic, igneous rock similar to granite but containing more plagioclase than potassium feldspar. Dacite is the volcanic equivalent.

Granoblastic : An arrangement of mineral grains in a rock of metamorphic origin similar to that of a normal granite, but produced by recrystallisation in the solid and not by crystallisation from a molten condition.

Granitoid : Any granite-like rock, including granodiorite, diorite, monzonite, and granite itself, among others.

Granite : A coarse-grained, often porphyritic, intrusive, felsic, igneous rock containing megascopic quartz, averaging 25%, much feldspar (orthoclase, microcline, sodic plagioclase) and mica or other coloured minerals. Rhyolite is the volcanic equivalent.

Graben : A depressed block of the Earth’s crust bordered by parallel faults.

Gondwanaland : The southern part of the supercontinent of Pangaea which eventually separated to form present-day South America, Africa, India, Australia and Antarctica.

Gneiss : A coarse-grained, pale-coloured gneissose rock, containing abundant feldspar with quartz, mica, hornblende, and garnet.

Glauconite : A green-coloured, hydrated silicate mineral of potassium and iron that forms on submerged banks. Its occurrence in sands and sandstones is considered an indication of accumulation under marine conditions.

Glass : A hard, brittle, transparent solid, such as used for windows, many bottles, or eyewear, including soda-lime glass, acrylic glass, sugar glass, isinglass (Muscovy-glass), or aluminium oxynitride.

Geosyncline : A mobile down-warping of the Earth’s crust, either elongate or basin-like, measured in scores of kilometres, which is subsiding as sedimentary and volcanic rocks accumulate to thicknesses of thousands of metres.

Geological time scale : Also geologic time scale.

Geologic map : A special-purpose map made to show geological features.

Gemology :Also spelled gemmology.

Gastrolith : A rock which is or was once held inside the digestive tract of a living animal.

Gabbro : A dark, coarse-grained, intrusive igneous rock chemically equivalent to basalt.

Fracture : Any crack or discontinuity. In its geological definition, it is only used when no displacement can be distinguished.

Fossiliferous : Bearing or being composed of fossils in rocks or strata.

Fossil : Any mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, or other once-living organisms.

Foliation : The parallel alignment of textural and structural features of a rock.