rock lying between or alternating with beds of a different kind of rock.Intrusion - body of igneous rock that has crystallized from molten magma below the surface of the Earth.Island arc - chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma.Isotope - different forms of an element each having different atomic mass (mass number).J[edit]Joint - discrete discontinuity surface without evidence of displacement. See also diaclase or bedding.Jurassic - major unit of the geologic timescale that extends from about 199.6 0.6 Ma (million years ago) to 145.4 4.0 Ma, the end of the Triassic to the beginning of the Cretaceous.K[edit]Ka - 1000 yearsKame - geological feature, 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.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.Karst - landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Characterised by closed depressions or sinkholes, caves and underground drainage.Kettle - 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.Kink - tight curl, twist, or bend in a rock band. See also folding and buckling.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.Kyanite - A silicate of aluminium which crystallises in the triclinic system. It usually occurs as long-bladed crystals, blue in colour, in metamorphic rocks.L[edit]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)Lamprophyres - 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-freeLava - molten rock expelled by a volcano during an eruption.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.Limestone - sedimentary rock composed largely of the mineral calcite (calcium carbonate: CaCO3).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.Lithic/Lithic fragment - 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.Lithification - the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock.Lithology - a description of the