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Glossary of Terms
Aeolian processes - Wind processes.
Cluster - A group of individual kimberlite pipes or dykes ranging in numbers from several to fifty. Generally the cluster has a diameter of approximately 40 km. Several clusters form a field, whereas several fields are commonly referred to as a province.
Craton - The portion of the continent that has not been subjected to major deformation since the Paleozoic Era.
Dyke - A kimberlite which has intruded into the earth's crustal fractures. Dykes are generally linear, 1-3 m wide and extend for several kilometres along a linear strike.
Gabbro - A plutonic rock consisting mainly of Ca-plagioclase and clinopyroxene. An extrusive equivalent of basalt.
Gneiss - A high grade metamorphosed granite with a course texture of mainly biotite and plagioclase.
Holocene, Miocene, Oligocene, Pleistocene, Pliocene,
Cretaceous - Geological time scales.
Hypabyssal - Defines an intrusive rock at depth intermediate between abyssal or plutonic and the surface (shallow depth). When applied to kimberlites, refers to dykes in the root zones of diatremes or to sills.
Isotherms - A line or surface connecting points of equal temperature.
Lamproite - Refers to a clan of peralkaline, typically ultrapotassic mafic to ultramafic rocks. Similar to kimberlites, they are hybrid rocks consisting of mixtures of primary magmatic constituents and upper mantle derived xenocrysts, including xenoliths.
Lithosphere - Solid outer portion of the earth including the crust and the portion of the upper mantle above the asthenosphere. Consists primarily of peridotite up to 175 km depth.
Macrocryst - A non-genetic term for relatively large (0.5 -10 mm), rounded to anhedral crystals set in kimberlite matrix.
Mantle - Zone of the earth below the crust and above the core (up to 3480 km). It is divided into the transition zone (up to 1000 km), the upper and lower mantle.
Metamorphic rock - A rock which has undergone physicochemical, mineralogical and structural changes when subjected to high temperature and pressure at depth within the earth's crust.
Metasomatism - Replacement of minerals by different ones within a rock by the slow action of percolating fluids.
Microdiamond - A diamond less than 0.5 mm in diameter.
Mobile Belt - A long, narrow crustal region characterised by present or past tectonic activity.
Peridotite - A plutonic rock consisting mainly of olivine and pyroxene.
Phenocryst - Crystal set in kimberlite matrix that have crystallised from the host magma.
Phyllite - A metamorphosed rock of grade intermediate between slate and schist.
Precambrian - The time preceding the Cambrian. It ranges from 4.7 Ga to 590 Ma. Generally associated with the time of the formation of the cratons.
Schist - A metamorphosed shale with layered texture due to muscovite crystals These are geological time scales.
Ventifacts - Stones shaped by wind in a desert area.
Xenocryst - A crystal foreign to the host magma and picked up from the wall rocks en route from melting to crystallization site. Xenocrysts may be derived from the mantle, or shallow depths.
Xenolith - A foreign inclusion in an igneous rock.
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