Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. Green olivine grains and purplish red garnet are visible. The sample is 13 cm (5 inches) long.

Kimberlite is a type of rock best known for sometimes containing diamonds. It is named after the town of Kimberley in South Africa, where the finding of a large kimberlite pipe in the 1870s spawned a diamond rush. Kimberlite has in many ways attracted more attention than its relative volume might suggest that it deserves. This is largely because it serves as a carrier of diamonds and garnet peridotite mantle xenoliths to the Earth's surface. Furthermore, its probable derivation from depths greater than any other igneous rock type, and the extreme magma composition that it reflects in terms of low silica content and high levels of incompatible trace element enrichment, make an understanding of kimberlite petrogenesis important. In this regard, the study of kimberlite has the potential to provide valuable information on the composition of the deep mantle, and melting processes occurring at or near the interface between the cratonic continental lithosphere and the underlying convecting asthenospheric mantle. Kimberlite occurs in the Earth's crust in vertical structures known as kimberlite pipes. Kimberlite pipes are the most important source of mined diamonds today. The general consensus reached on kimberlites is that they are formed deep within the mantle, at between 150 and 450 kilometres depth, from anomalously enriched exotic mantle compositions, and are erupted rapidly and violently, often with considerable carbon dioxide and other volatile components. It is this depth of melting and generation which makes kimberlites prone to hosting diamond xenocrysts. Photograph by Gregory Phillips. ... Photograph by Gregory Phillips. ... James Bay in summer 2000 James Bay (French, Baie James) is a large body of water on the southern end of Hudson Bay in Canada. ... Motto: Ut Incepit Fidelis Sic Permanet (Latin: Loyal she began, loyal she remains) Capital Toronto Largest city Toronto Official languages English (de facto) Government Lieutenant-Governor David C. Onley Premier Dalton McGuinty (Liberal) Federal representation in Canadian Parliament House seats 107 Senate seats 24 Confederation July 1, 1867 (1st) Area... Rock redirects here. ... This article is about the mineral. ... The Big Hole, a prominent tourist attraction in Kimberley Kimberley is a town in South Africa, and the capital of the Northern Cape. ... Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. ... Peridotite xenolith from San Carlos, southwestern United States. ... Earth cutaway from core to exosphere. ... A xenolith A xenolith (Greek: foreign rock) is a rock fragment which becomes enveloped in a larger rock during the latters development and hardening. ... Volcanic rock in North America Plutonic rock in North America Igneous rocks (etymology from Latin ignis, fire) are rocks 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. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Microminerals (also known as trace elements) are micronutrients that are chemical elements. ... Petrogenesis, also known as petrogeny, is a branch of petrology dealing with the origin of igneous rocks. ... World geologic provinces. ... The tectonic plates of the Lithosphere on Earth. ... This article does not cite any references or sources. ... Earth cutaway from core to exosphere. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Volatiles are that group of compounds with low boiling points (see volatile) that are associated with a planets or moons crust and/or atmosphere. ... A xenolith A xenolith (Greek: foreign rock) is a rock fragment which becomes enveloped in a larger rock during the latters development and hardening. ...

Morphology and volcanology

Kimberlites are found as dikes and volcanic pipes which underlie and are the source for rare and relatively small explosive volcanoes (maars). Kimberlites in the Guyana Shield, in Venezuela and French Guyana, form thin, tabular dipping sills. A dike in geology refers to a tabular intrusive igneous body. ... Volcanic Pipe Volcanic pipes are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. ... Ukinrek Maars, Alaska; the result of a 10-day eruption in 1977. ... Mt Roraima in Guyana The Guiana Shield (Spanish: Guayana) forms a portion of the northern coast of South America. ... In geology, a sill is a tabular, often horizontal mass of igneous rock that has been intruded laterally between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. ...

Kimberlite pipes are the result of explosive diatreme volcanism from very deep mantle derived sources. These volcanic explosions produce vertical columns of rock that rise from deep magma reservoirs. The morphology of kimberlite pipes is varied but generally includes a sheeted dyke complex of tabular, vertically dipping feeder dykes in the root of the pipe which extends down to the mantle. Within 1.5-2 km of the surface the highly pressured magma explodes upwards and expands to form a conical to cylindrical diatreme, which erupts to the surface. The surface expression is rarely preserved but is usually similar to a maar volcano. The diameter of a kimberlite pipe at the surface is typically a few hundred meters to a kilometer. Volcanic Pipe Volcanic pipes are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. ... This article is about volcanoes in geology. ... Earth cutaway from core to exosphere. ... A Diatreme is a volcanic pipe or feature formed by a gas or volatile rich explosive magma. ...

Many kimberlite pipes are believed to have formed about 70 to 150 million years ago, but in Southern Africa, there are several formed between 60 to 1600 million years ago^[1].

Two Jurassic kimberlite dikes exist in Pennsylvania. One, the Gates-Adah Dike, outcrops on the Monongahela River on the border of Fayette and Greene Counties. The other, the Dixonville-Tanoma Dike in central Indiana County, does not outcrop at the surface and was discovered by miners.^[1] The Jurassic Period is a major unit of the geologic timescale that extends from about 199. ... A dike in geology refers to a tabular intrusive igneous body. ... This article is about the U.S. State. ... The South Tenth Street Bridge over the Monongahela River in Pittsburgh in 2005 The Monongahela River in Fairmont, West Virginia in 2006 Monongahela River Scene, 1857[11] Opekiska Lock and Dam on the Monongahela River near Fairmont, West Virginia at river mile 115 The Monongahela River (pronounced , also known locally... Fayette County is a county located in the U.S. state of Pennsylvania. ... Greene County is a county located in the state of Pennsylvania. ... Indiana County is a county located in the U.S. state of Pennsylvania. ...

Petrographic characters

Kimberlites are a clan of volatile-rich (dominantly carbon dioxide) potassic ultramafic rocks. Commonly, they exhibit a distinctive inequigranular texture resulting from the presence of rounded, anhedral and fragmented macrocrysts (0.5-10 mm) and in some instances megacrysts (10-200 mm) set in a fine grained matrix. The megacryst/macrocryst assemblage consists of rounded anhedral crystals of magnesian ilmenite, chromium-poor titanian pyrope, olivine, Cr-poor clinopyroxene, phlogopite, enstatite and titanium-poor chromite. Olivine is the dominant member of the macrocryst assemblage. The matrix minerals may include: second generation euhedral primary olivine and/or phlogopite, together with perovskite, spinel (titaniferous magnesian aluminous chromite, titanian chromite, members of the magnesian ulvospinel-ulvospinel-magnetite series), diopside (Al- and Ti- poor), monticellite, apatite, calcite, and primary late-stage serpentine (commonly Fe rich). Some kimberlites contain late-stage poikilitic eastonite phlogopites. Nickeliferous sulphides and rutile are common accessory minerals. The replacement of early-formed olivine, phlogopite, monticellite, and apatite by deuteric serpentine and calcite is common. Evolved members of the clan may be devoid of, or poor in, macrocrysts, and composed essentially of calcite, serpentine, and magnetite together with minor phlogopite, apatite and perovskite. Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ... In geometry, the dihedral is the angle between two planes. ... The matrix or groundmass of an igneous rock consists of fine grained often microscopic crystals in which larger crystals (phenocrysts) are embedded. ... For other uses, see Crystal (disambiguation). ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... Ilmenite is a weakly magnetic iron-black or steel-gray mineral found in metamorphic and igneous rocks. ... REDIRECT [[ Insert text]]EWWWWWWWWWWWWW YO General Name, symbol, number chromium, Cr, 24 Chemical series transition metals Group, period, block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ... The pyrope is a garnet. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Phlogopite is a yellow, greenish or reddish brown member of the mica family of phyllosilicates. ... The pyroxene silicate minerals enstatite (MgSiO3) and ferrosilite (FeSiO3) form a complete solid solution series and are common rock-forming minerals found in igneous and metamorphic rocks and meteorites. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... Chromite, iron magnesium chromium oxide: (Fe,Mg)Cr2O4, is an oxide mineral belonging to the spinel group. ... Euhedral refers to well formed crystals with sharp easily recognised faces. ... Perovskite (calcium titanium oxide, CaTiO3) is a relatively rare mineral occurring in orthorhombic (pseudocubic) crystals. ... The spinels are any of a class of minerals which crystallize in the isometric system with an octahedral habit. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... ... Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. ... Diopside Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. ... Monticellite and kirschsteinite are gray silicate minerals of the olivine group which composition CaMgSiO4 and CaFeSiO4, respectivly. ... Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal. ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... For other uses, see Serpentine (disambiguation). ... Poikilitic texture refers to crystals, typically phenocrysts, in an igneous rock which contain small grains of other minerals. ... For other uses, see Nickel (disambiguation). ... In chemistry, a sulfide (sulphide in British and Canadian English) is a combination of sulfur with an oxidation number of -2, with another chemical element or a radical thereof. ... Rutile is a mineral composed primarily of titanium dioxide, TiO2. ...

Petrogenesis

Since the discovery of diamonds in kimberlite many different theories regarding the processes involved in kimberlite formation have been put forward Here we will examine 2 theories: 1) the magmatic theory and 2) the hydrovolcanic theory. 1) Magmatic (Fluidization) Theory: The original proponent of this theory was Dawson (1962, 1971). It was subsequently built upon by Clement (1982) and is presently being pushed by Field and Scott Smith (1999). A brief outline of the magmatic/fluidization theory is as follows. Kimberlite magma rises from depth with different pulses building what are termed 'embryonic pipes' (Mitchell, 1986) on top of each other. The result is a complex network of overlapping embryonic pipes of hypabyssal facies kimberlite. The surface is not breached and the volatiles do not escape. At some point the embryonic pipes reach a shallow enough depth (~500 meters) whereby the pressure of the volatiles is able to overcome the load of the overlying rock and the volatiles escape. As the volatiles are escaping, a brief period of fluidization ensues. This involves the upward movement of volatiles which are sufficiently fast to 'fluidize' the kimberlite and fragmented host rock so that particles are entrained in a gas-solid-liquid medium. Fragments of country rock found in this fluidized system may sink depending on their density. The fluidized front moves downwards from the initial depth. Fluidization is believed to be short lived as fragments are commonly angular.

This theory is suppose explains features seen in kimberlite pipes such as: i) fragments of country rock found as much as 1 km below their stratigraphic level through fluidization. ii) steep-sided pipes with angles ~80-85 degrees. As the initial explosion is at a relatively shallow depth (~500m) the surface radii to depth ratio will be closer to 1. iii) complex network of pipes of hypabyssal facies found at depth. iv) the transition from hypabyssal facies to diatreme facies. Country rock is a geological term meaning the rock native to an area. ... Lithostratigraphy is the geological science associated with the study of stratum or rock layers. ... The term facies was introduced by the Swiss geologist Amanz Gressly in 1838 and was part of his significant contribution to the foundations of modern stratigraphy (see Cross and Homewood 1997), which replaced the earlier notions of Neptunism. ...

2) Hydrovolcanic (Phreatomagmatic) Theory: The main proponent of this theory is Lorenz (1999), who has pushed the hydrovolcanic model for 3 decades. Kimberlite magmas rise from depth through narrow ~1m thick fissures. Either the kimberlite magma is focused along structural faults which act as focuses for waters, or, the resultant brecciation due to volatile exsolution from the rising kimberlite may act as a focus for water. In any case, the near surface environment is rich in water and the interaction of the rising hot magma with the cool water produces a pheatomagmatic explosion. The explosion is short lived. The brecciated rock becomes recharged with groundwater. Another pulse of kimberlite magma follows the same structural weaknesses in the rock to surface and again comes in contact with water producing another explosion. Subsequent pulses react with water in the same way while the contact front moves downwards to the average depth of hypabyssal facies/diatreme facies transitions. Phreatic eruption at the summit of Mount St. ... A binary phase diagram displaying solid solutions over the full range of relative concentrations. ... Breccia, derived from the Latin word for broken, is a sedimentary rock composed of angular fragments in a matrix that may be of a similar or a different material. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. ...

Chemical characteristics

Kimberlites and orangeites are complex hybrids in which an underminable quantity of foreign and cumulate material has been integrated, disaggregated, and variably absorbed into the liquid. It is thus difficult, if not impossible, to determine what constituents are components of the original melt, and what has been incorporated en route to the surface. Thus the nature of the primitive liquids is largely unknown. This hybrid nature presents an obvious problem when it comes to interpreting the geochemistry. Differentiation process lead to the concentration of macrocryst + phenocryst phases and evolved liquids, eventually resulting in the evolution of carbonate- rich residua. Major element concentrations thus vary widely as a result of both contamination, accumulation and fractionation processes. Variation in phenocryst composition suggests that Kimberlites are commonly mixtures that result from the coalescence of smaller magma batches as they rise.

Major Oxides Composition of Kimberlite includes following oxides:- (a) SiO2 (b) TiO2 (c) Al2O3 (d) FeO (e) MnO (f) MgO (g) CaO (h) Na2O (i) K2O (j) P2O5 Late stages of intrusion commonly take the form of crystal-liquid slurry in which the relative proportions of the constituent minerals might easily vary. Therefore there is wide variation in SiO2, CaO, MgO, CO2 and H2O. There is a low concentration of Al2O3 and Na2O.

Trace Elements Trace elements associated with Kimberlites are:- Sc, V, Cr, Ni, Co, Cu, Zn, Ba, Sr, Zr, Hf, Nb, Ta, Th, U, La and Yb Due to the mantle source of Kimberlite high levels of compatible trace elements (Ni, Cr, Sc, V, Co, Cu, Zn) are present.

Average Analysis and Compositional Ranges of Kimberlites and Orangeites.

 Kimberlite Orangeite SiO2 33.0 27.8-37.5 35.0 27.6-41.9 TiO2 1.3 0.4-2.8 1.1 0.4-2.5 Al2O3 2.0 1.0-5.1 2.9 0.9-6.0 FeO* 7.6 5.9-12.2 7.1 4.6-9.3 MnO 0.14 0.1-0.17 0.19 0.1-0.6 MgO 34.0 17.0-38.6 27. 10.4-39.8 CaO 6.7 2.1-21.3 7.5 2.9-24.5 Na2O 0.12 0.03-0.48 0.17 0.01-0.7 K2O 0.8 0.4-2.1 3.0 0.5-6.7 P2O5 1.3 0.5-1.9 1.0 0.1-3.3 LOI 10.9 7.4-13.9 11.7 5.2-21.5 Sc 14 20 V 100 95 Cr 893 1722 Ni 965 1227 Co 65 77 Cu 93 28 Zn 69 65 Ba 885 3164 Sr 847 1263 Zr 263 268 Hf 5 7 Nb 171 120 Ta 12 9 Th 20 28 U 4 5 La 150 186 Yb 1 1 

Kimberlitic indicator minerals

Kimberlites are peculiar igneous rocks because they contain a variety of mineral species with peculiar chemical compositions. These minerals such as potassic richterite, chromian diopside (a pyroxene), chromium spinels, magnesian ilmenite, and garnets rich in pyrope plus chromium are generally absent from most other igneous rocks, making them particularly useful as indicators for kimberlites. Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... The pyrope is a garnet. ...

These indicator minerals are generally sought in stream sediments in modern alluvial material. Their presence, when found, may be indicative of the presence of a kimberlite within the erosional watershed which has produced the alluvium. Alluvium (from the Latin, alluvius, from alluere, to wash against) is soil or sediments deposited by a river or other running water. ...

Main minerals of Kimberlite

1. Macrocrysts of olivine,
2. Picroilmenite,
3. Cr-diopside,
4. Pyrope garnet;
5. Phenocrysts of olivine and
6. Microphenocrysts of monticellite,perovskite, kinoshitalite mica
7. Spinel in a calcite + serpentine matrix.

Common accessory minerals

1. Nickeliferous sulphides
2. Rutile

The geochemistry of Kimberlites is defined by the following parameters;

• Ultramafic; MgO >12% and generally >15%
• Ultrapotassic; Molar K2O/Al2O3 >3
• Near-primitive Ni (>400ppm), Cr (>1000ppm), Co (>150ppm)
• REE-enrichment
• Moderate to high LILE enrichment; ΣLILE = >1,000ppm
• High H2O and CO2

Economic importance

Kimberlites are the most important source of primary diamonds. Many kimberlite pipes also produce rich alluvial or eluvial diamond placer deposits. However, only about 1 in 200 kimberlite pipes contain gem-quality diamonds. This article is about the gemstone. ... Alluvium is soil land deposited by a river or other running water. ... In geology, eluvium or eluvial deposits are those geological deposits and soils that are derived by in situ weathering or weathering plus gravitational movement or accumulation. ... In geology, a placer deposit is a deposit of earth, sand, or gravel, containing valuable minerals in particles, especially by the side of a river, or in the bed of a mountain stream. ...

The deposits occurring at Kimberley, South Africa were the first recognized and the source of the name. The Kimberley diamonds were originally found in weathered kimberlite which was colored yellow by limonite, and so was called yellow ground. Deeper workings encountered less altered rock, serpentinized kimberlite, which miners call blue ground. Kimberley is a town in South Africa, and the capital of the Northern Cape. ... This article is about the mineral. ... Weathering is the decomposition of rocks, soils and their minerals through direct contact with the Earths atmosphere. ... Limonite Limonite Limonite is a ferric hydrate of varying composition, the generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as Limonite often contains a varying amount of oxide compared to hydroxide. ... A sample of serpentinite rock, partially made up of chrysotile Serpentinite is a rock comprised of one or more serpentine minerals. ... Blue Ground generally refers to a laver of nonoxidized kimberlite. ...

Related rock types

• Lamproite
• Lamprophyre
• Nepheline syenite
• Ultrapotassic igneous rocks
• Kalsititic rocks

Lamproite is a peralkaline volcanic rock. ... Lamprophyres (Greek Lampros, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals) are a group of rocks containing phenocrysts, usually of biotite and hornblende (with bright cleavage surfaces), often also of olivine and augite, but not of feldspar. ... Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. ... Ultrapotassic igneous rocks are a class of rare, volumetrically minor generally ultramafic or mafic silica-depleted igneous rocks. ...

References

• Kimberlite
• Kimberlite hosted diamonds