"Lake Ellen Kimberlite The Lake Ellen Kimberlite is a poorly exposed volcanic breccia located about northeast of Crystal Falls in the Upper Peninsula of Michigan. The first publication in 1981 describing the feature led to speculation that this or similar kimberlites in the area might have been the source of the diamonds discovered a century before in Wisconsin as well as a period of exploration by several minerals firms. The kimberlite was discovered in 1971 when a logging road was bulldozed through the area exposing the unusual looking rock. The exposure consists of several small areas otherwise overlain by glacial"
"Hence, he reclassified group II kimberlites as orangeites to prevent confusion. Group-I kimberlites are of CO-rich ultramafic potassic igneous rocks dominated by primary forsteritic olivine and carbonate minerals, with a trace-mineral assemblage of magnesian ilmenite, chromium pyrope, almandine-pyrope, chromium diopside (in some cases subcalcic), phlogopite, enstatite and of Ti-poor chromite. Group I kimberlites exhibit a distinctive inequigranular texture caused by macrocrystic () to megacrystic () phenocrysts of olivine, pyrope, chromian diopside, magnesian ilmenite, and phlogopite, in a fine- to medium-grained groundmass. The groundmass mineralogy, which more closely resembles a true composition of the igneous rock, is dominated by carbonate and"
"till. Magnetic survey work done in 1956 depicts an elliptical positive anomaly long in an east–west direction and wide, which probably defines the limits of the pipe. The kimberlite is intruded into volcanic rocks of the Proterozoic Hemlock Formation. The exposed material is grayish green to reddish, iron stained highly weathered and consists of disaggregated rubbly fragments up to . It is generally accepted that the pipe was emplaced about 180 million years ago. The lake Ellen Kimberlite is popular with rock hounds as the classic indicator minerals (pyrope, magnesian ilmenite and chrome diopside) for kimberlite are easily found in"
"as analcite, prehnite, natrolite, scolecite, chabazite, heulandite, etc. Ultramafic tuffs are extremely rare; their characteristic is the abundance of olivine or serpentine and the scarcity or absence of feldspar and quartz. Rare occurrences may include unusual surface deposits of maars of kimberlites of the diamond-fields of southern Africa and other regions. The principal rock of kimberlite is a dark bluish-green, serpentine-rich breccia (blue-ground) which when thoroughly oxidized and weathered becomes a friable brown or yellow mass (the ""yellow-ground""). These breccias were emplaced as gas–solid mixtures and are typically preserved and mined in diatremes that form intrusive pipe-like structures. At depth,"
"Comendite Comendite is a hard, peralkaline igneous rock, a type of light blue grey rhyolite. Phenocrysts are sodic sanidine with minor albite and bipyramidal quartz. Comendite occurs in the mountains Tibrogargan, Coonowrin, Tunbubudla, Coochin, Saddleback, Tibberoowuccum and Ngungun in the Glass House Mountains, South East Queensland, Australia. The blue colour is caused by very small crystals of riebeckite or arfvedsonite. Comendite also occurs in Sardinia, Corsica, Ascension Island, Ethiopia, Somalia and other areas of East Africa. The 1903 eruption of Changbaishan volcano in north-east China erupted comendite pumice. Comendite derives its name from the area of Le Commende on San"
"Pietro Island in Italy, where the rock type is found. Comendite Comendite is a hard, peralkaline igneous rock, a type of light blue grey rhyolite. Phenocrysts are sodic sanidine with minor albite and bipyramidal quartz. Comendite occurs in the mountains Tibrogargan, Coonowrin, Tunbubudla, Coochin, Saddleback, Tibberoowuccum and Ngungun in the Glass House Mountains, South East Queensland, Australia. The blue colour is caused by very small crystals of riebeckite or arfvedsonite. Comendite also occurs in Sardinia, Corsica, Ascension Island, Ethiopia, Somalia and other areas of East Africa. The 1903 eruption of Changbaishan volcano in north-east China erupted comendite pumice. Comendite derives"
"Ijolite Ijolite is an igneous rock consisting essentially of nepheline and augite. Ijolite is a rare rock type of considerable importance from a mineralogical and petrological standpoint. The word is derived from the first syllable of the Finnish words such as ""Iivaara"", ""Iijoki"", common as geographical names in Finland, and the Ancient Greek ""Xiflos"", a stone. Ijolite occurs in various parts of the Kainuu region of eastern Finland and in the Kola Peninsula of northwest Russia on the shores of the White Sea. Ijolite was first defined and named by Finnish geologist Wilhelm Ramsay. The pyroxene is , yellow or"
"for German explorer Emil Riebeck (1853–1885). It typically forms dark-blue elongated to fibrous crystals in highly alkali granites, syenites, rarely in felsic volcanics, granite pegmatites and schist. It occurs in banded iron formations as the asbestiform variety ""crocidolite"" (blue asbestos). It occurs in association with aegirine, nepheline, albite, arfvedsonite in igneous rocks; with tremolite, ferro-actinolite in metamorphic rocks; and with grunerite, magnetite, hematite, stilpnomelane, ankerite, siderite, calcite, chalcedonic quartz in iron formations. The riebeckite granite known as ""ailsite"", found on the island of Ailsa Craig in western Scotland, is prized for its use in the manufacture of curling stones. Riebeckite"
"Ignimbrite Ignimbrite is a variety of hardened tuff. Ignimbrites are igneous rocks made up of crystal and rock fragments in a glass-shard groundmass, albeit the original texture of the groundmass might be obliterated due to high degrees of welding. The term ""ignimbrite"" is not recommended by the IUGS Subcommission on the Systematics of Igneous Rocks. Ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, which is a hot suspension of particles and gases flowing rapidly from a volcano and driven by being denser than the surrounding atmosphere. New Zealand geologist Patrick Marshall (1869-1950) derived the term ""ignimbrite"""
"shales interbedded with kimberlite at some of the diatremes are consistent with a Late Cretaceous age (Late Albian to Maastrichtian). The volcanic rocks of the BM field consist primarily of crater-facies pyroclastic kimberlite and resedimented kimberlite. They include massive layers, as well as bedded and graded layers of coarse lapilli alternating with layers of finer tuff. Lapilli and olivine phenocrysts are set in a grey-green matrix of serpentine, carbonate minerals (calcite, dolomite and magnesite) and clay minerals. Phlogopite, oxide minerals (ilmenite, perovskite and spinel), apatite and pyrite are also present. Diamonds and microdiamonds have been recovered from samples taken from"
"Elliott County Kimberlite The Elliott County Kimberlite (Sometimes called the Ison Creek Kimberlite) was discovered in Elliott County, Kentucky, by Albert R. Crandall in 1884 over two years before Carvill Lewis named a similar porphyritic peridotite occurring near Kimberley, South Africa, a kimberlite. It occurs as three separate elongate intrusive bodies 1/4 to 1/2 mi in length and a few hundred feet in width, within an area of about a square mile. The rock is a dark-green peridotite (kimberlite) composed of serpentinized olivine and a number of accessory minerals, including phlogopite, pyrope, calcite, enstatite, magnesian ilmenite, and others. Xenoliths, mainly"
"during the large Amakinsky Expedition in Yakut ASSR. They found traces of the volcanic rock kimberlite, which is usually associated with diamonds. This finding was the second success in the search for kimberlite in Russia, after numerous failed expeditions of the 1940s and 1950s. (The first was Zarnitsa mine, 1954.) For this discovery, in 1957 Khabardin was given the Lenin Prize, one of the highest awards in the Soviet Union. The development of the mine started in 1957, in extremely harsh climate conditions. Seven months of winter per year froze the ground, making it hard to mine. During the brief"
"of the Richat Structure. The kimberlite plug has been dated to around 99 million years old. These intrusive igneous rocks are interpreted as indicating the presence of a large alkaline igneous intrusion that currently underlies the Richat Structure and created it by uplifting the overlying rock. Spectacular hydrothermal features are a part of the Richat Structure. They include the extensive hydrothermal alteration of rhyolites and gabbros and a central megabreccia created by hydrothermal dissolution and collapse. The siliceous megabreccia is at least 40 m thick in its center to only a few meters thick along its edges. The breccia consists"
"Quartzolite Quartzolite or silexite is an intrusive igneous rock, in which the mineral quartz is more than 90% of the rock's felsic mineral content, with feldspar at up to 10%. Typically, quartz forms more than 60% of the rock, the rest being mostly feldspar although minor amounts of mica or amphibole may also be present. Quartzolite occurs as dykes, sills, veins, bosses and segregation masses. It is an extremely rare type of rock. No extrusive rock equivalent of quartzolite is known. Quartzolite is found in association with greisen and pegmatite. The use of the synonym """"silexite"""" is discouraged because it"
"Quartzolite Quartzolite or silexite is an intrusive igneous rock, in which the mineral quartz is more than 90% of the rock's felsic mineral content, with feldspar at up to 10%. Typically, quartz forms more than 60% of the rock, the rest being mostly feldspar although minor amounts of mica or amphibole may also be present. Quartzolite occurs as dykes, sills, veins, bosses and segregation masses. It is an extremely rare type of rock. No extrusive rock equivalent of quartzolite is known. Quartzolite is found in association with greisen and pegmatite. The use of the synonym """"silexite"""" is discouraged because it"
"with the diopside. Olivines are surrounded by chromite. Olivines characterize the texture of the Igwisi rocks, where they form spherical inclusions. The olivines are primarily forsteritic in composition. Inclusions in the kimberlite include skeletal apatite, stellate aragonite and calcite. High concentrations of are found in the rock, which may have resulted in the depolymerization of the melt, increasing its fluidity and resulting in effusive activity. Peridotite xenoliths originate from of depth. Spinels in the groundmass suggest that crustal contamination was extensive. The geochemistry suggests an origin at high pressures (depths of ) and equilibrium temperatures of . Rainfall has subsequently"
"some distance from any stream or river, in hard rock called blue ground, later called kimberlite, after the mining town of Kimberley where the diamond diggings were concentrated. The diggings were located in an area of vague boundaries and disputed land ownership. Claimants to the site included the South African (Transvaal) Republic, the Orange Free State Republic, and the mixed-race Griqua nation under Nicolaas Waterboer. Cape Colony Governor Sir Henry Barkly persuaded all claimants to submit themselves to a decision of an arbitrator and so Robert W Keate, Lieutenant-Governor of Natal was asked to arbitrate. Keate awarded ownership to the"
"(especially when impregnating quartz); lazulite; smithsonite; hemimorphite; wardite; and a fossil bone or tooth called odontolite or ""bone turquoise"", coloured blue naturally by the mineral vivianite. While rarely encountered today, odontolite was once mined in large quantities—specifically for its use as a substitute for turquoise—in southern France. These fakes are detected by gemologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both colour"
"Aenigmatite Aenigmatite, also known as ""Cossyrite"" after Cossyra, the ancient name of Pantelleria, is a sodium, iron, titanium inosilicate mineral. The chemical formula is NaFeTiSiO and its structure consists of single tetrahedral chains with a repeat unit of four and complex side branches. It forms brown to black triclinic lamellar crystals. It has Mohs hardness of 5.5 to 6 and specific gravity of 3.74 to 3.85. Aenigmatite forms a solid-solution series with wilkinsonite, NaFeFeSiO. Aenigmatite is primarily found in peralkaline volcanic rocks, pegmatites, and granites as well as silica-poor intrusive rocks. It was first described by August Breithaupt in 1865"
"which it is enveloped; an included rock of similar type is called an ""autolith"" or a cognate inclusion. Xenoliths and xenocrysts provide important information about the composition of the otherwise inaccessible mantle. Basalts, kimberlites, lamproites and lamprophyres, which have their source in the upper mantle, often contain fragments and crystals assumed to be a part of the originating mantle mineralogy. Xenoliths of dunite, peridotite and spinel lherzolite in basaltic lava flows are one example. Kimberlites contain, in addition to diamond xenocrysts, fragments of lherzolites of varying composition. The aluminium-bearing minerals of these fragments provide clues to the depth of origin."
"content, but at Þingmúli the opposite was true, leading Carmichael to the conclusion that the iron-rich intermediate rock deserved its own name, ""icelandite."" Icelandite Icelandite is a type of volcanic rock, an iron rich, aluminium lacking andesite. Icelandites are between rhyodacite and tholeiitic basalt in composition and contain andesine, hypersthene and augite, with a silica (SiO) content greater than 60%. The name was coined by the British geologist Ian S. E. Carmichael (who later became professor at the University of California, Berkeley) while working around 1960 on his PhD thesis at a Cenozoic volcano near the parsonage Thingmuli (Þingmúli) in"
"as a rare component within ultramafic nodules in kimberlites in association with olivine, enstatite, chrome diopside, chromian pyrope, chromian spinel, ilmenite, perovskite, zircon, diamond, omphacite, rutile, carbonates and micas. It has been reported from the Red Ledge mine in Nevada County, California in addition to the type location in Lesotho. Knorringite is a tracer mineral in the search for diamonds in kimberlite pipes. Knorringite Knorringite is a mineral species belonging to the garnet group, and forms a series with the species pyrope. It was discovered in 1968 in the Kao kimberlite pipe in the Butha-Buthe District of Lesotho and is"
"all over the continent. The immigrants were accepted with open arms, because the De Beers company was in search of cheap labour to help run the mines. Another group drawn to the city for money was prostitutes, from a wide variety of ethnicities who could be found in bars and saloons. It was praised as a city of limitless opportunity. Five big holes were dug into the earth following the kimberlite pipes, which are named after the town. Kimberlite is a diamond-bearing blue ground that sits below a yellow colored soil. The largest, The Kimberley mine or ""Big Hole"" covering"
"igneous rocks, nepheline syenite, melilitite, kimberlites and rare carbonatites. Perovskite is a common mineral in the Ca-Al-rich inclusions found in some chondritic meteorites. A rare-earth-bearing variety ""knopite"" (Ca,Ce,Na)(Ti,Fe)O) is found in alkali intrusive rocks in the Kola Peninsula and near Alnö, Sweden. A niobium-bearing variety ""dysanalyte"" occurs in carbonatite near Schelingen, Kaiserstuhl, Germany. The stability of perovskite in igneous rocks is limited by its reaction relation with sphene. In volcanic rocks perovskite and sphene are not found together, the only exception being in an etindite from Cameroon. Perovskites have a cubic structure with general formula of . In this structure,"
"Cumberlandite Cumberlandite is the state rock of the U.S. state of Rhode Island. It is only found in large concentrations on a lot in Blackstone Valley, Cumberland, and in traces scattered throughout the Narragansett Bay watershed. Due to its high amounts of iron, it is slightly magnetic. The rocks were discovered by settlers hundreds of years ago, and were initially deemed valuable for the manufacture of cannon and farm tools in the 18th and 19th centuries. The rock also contains a relatively high level of titanium, also valuable for the manufacture of tools. Colonists tried to make cannon from the"
"Icelandite Icelandite is a type of volcanic rock, an iron rich, aluminium lacking andesite. Icelandites are between rhyodacite and tholeiitic basalt in composition and contain andesine, hypersthene and augite, with a silica (SiO) content greater than 60%. The name was coined by the British geologist Ian S. E. Carmichael (who later became professor at the University of California, Berkeley) while working around 1960 on his PhD thesis at a Cenozoic volcano near the parsonage Thingmuli (Þingmúli) in East Iceland. For continental cogenetic series of volcanic rocks it is generally the case that the concentration of iron decreases with increasing silica"
"Danish archaeologist Thorkild Ramskou suggested in 1967 that the ""sun-stones"" referred to in some sagas might have been natural crystals capable of polarizing skylight. The mineral cordierite occurring in Norway has the local name ""Viking's Compass."" Its changes in colour would allow determining the sun's position (azimuth) even through an overcast or foggy horizon. The sunstones are doubly refracting, meaning that objects viewed through them can be seen as double because of positively charged calcium ions and negatively charged carbonate ions. When looking at the sun the stone, it will project two overlapping shadows on the crystal. The opacities of"
"elements not found in abundance in normal igneous rocks. Minerals containing lithium, rubidium, beryllium, boron, niobium, tantalum, tin, bismuth, fluorine and other elements can be found. The term ""miarolitic"" comes from the Italian ""miarole"" in reference to the mineral-rich pegmatite region of Baveno and Cuasso al Monte in northern Italy. Miarolitic cavity Miarolitic cavities (or ""miarolitic texture"") are typically crystal-lined irregular cavities or vugs most commonly found in granitic pegmatites, and also in a variety of igneous rocks. The central portions of pegmatites are often miarolitic as the pegmatite dike crystallizes from the outside walls toward the center. The volatile"
"optic angle is 58° to 63°. Diopside is found in ultramafic (kimberlite and peridotite) igneous rocks, and diopside-rich augite is common in mafic rocks, such as olivine basalt and andesite. Diopside is also found in a variety of metamorphic rocks, such as in contact metamorphosed skarns developed from high silica dolomites. It is an important mineral in the Earth's mantle and is common in peridotite xenoliths erupted in kimberlite and alkali basalt. Diopside is a precursor of chrysotile (white asbestos) by hydrothermal alteration and magmatic differentiation; it can react with hydrous solutions of magnesium and chlorine to yield chrysotile by"
"Nuummite Nuummite is a rare metamorphic rock that consists of the amphibole minerals gedrite and anthophyllite. It is named after the area of Nuuk in Greenland, where it was found. Nuummite is usually black in colour and opaque. It consists of two amphiboles, gedrite and anthophyllite, which form exsolution lamellae that give the rock its typical iridescence. Other common minerals in the rock are pyrite, pyrrhotite and chalcopyrite, which form shimmering yellow bands in polished specimens. In Greenland the rock was formed by two consecutive metamorphic overprints of an originally igneous rock. The intrusion took place in the Archean around"
"which may form. Till may contain detectable concentrations of gems or other valuable ore minerals picked up by the glacier during its advance, for example the diamonds found in the U.S. states of Wisconsin, Indiana, and in Canada. Prospectors use trace minerals in tills as clues to follow the glacier upstream to find kimberlite diamond deposits and other types of ore deposits. In cases where till has been indurated or lithified by subsequent burial into solid rock, it is known as the sedimentary rock ""tillite"". Matching beds of ancient tillites on opposite sides of the south Atlantic Ocean provided early"
"few millimeters in length. Other minerals identified were dark green, pyroxene crystals with 70 percent hedenbergite and 30 percent diopside; white aggregates of tridymite; brown, granular olivine crystals with 80 percent forsterite and 20 percent fayalite; and tiny black, hexagonal plates of hematite with beveled edges. These minerals constitute a rare combination, and Trimble (1963) was unable to explain why free silica tridymite would be found together with low silica olivine. The hill descends to meet the floodplain of the Columbia River, and at lower elevations, the mountain has cliffs on its northern and eastern sides. At the foot of"
"than . Weak pyroclastic activity probably accompanied the eruptive activity. Presumably, low intensity explosive activity built the cones, starting from the northeast cone and ending with the southwest cone. Afterwards, lava flows were generated. The Igwisi Hills are the only places in the world where possible kimberlite lava flows have been found, in form of calcite-olivine lavas. Kimberlite tuffs are also found, a rare species which is very susceptible to erosion. True kimberlites are usually very old eruptive rocks, consequently any subsurface volcanic structure has long since been eroded away. These kimberlites were erupted in a fairly nonexplosive fashion. Not"