Pigeonite

Pigeonite is a mineral in the clinopyroxene subgroup of the pyroxene group. It has a general formula of (Ca,Mg,Fe)(Mg,Fe)Si2O6. The calcium cation fraction can vary from 5% to 25%, with iron and magnesium making up the rest of the cations.

Pigeonite crystallizes in the monoclinic system, as does augite, and a miscibility gap exists between the two minerals. At lower temperatures, pigeonite is unstable relative to augite plus orthopyroxene. The low-temperature limit of pigeonite stability depends upon the Fe/Mg ratio in the mineral and is hotter for more Mg-rich compositions; for a Fe/Mg ratio of about 1, the temperature is about 900 °C. The presence of pigeonite in an igneous rock thus provides evidence for the crystallization temperature of the magma, and hence indirectly for the water content of that magma.

Pigeonite is found as phenocrysts in volcanic rocks on Earth and as crystals in meteorites from Mars and the Moon. In slowly cooled intrusive igneous rocks, pigeonite is rarely preserved. Slow cooling gives the calcium the necessary time to separate itself from the structure to form exsolution lamellae of calcic clinopyroxene, leaving no pigeonite present.[4] Textural evidence of its breakdown to orthopyroxene plus augite may be present, as shown in the accompanying microscopic image.

Pigeonite is named for its type locality on Lake Superior's shores at Pigeon Point, Minnesota, United States. It was first described in 1900.[3][5]

Pigeonite
PyroxeneExsol 0.5mmm
Polarized light microscope image of part of a grain of orthopyroxene containing exsolution lamellae of augite The texture documents a multistage history: (1) crystallization of twinned pigeonite, followed by exsolution of augite; (2) breakdown of pigeonite to orthopyroxene plus augite; (3) exsolution of augite parallel to the former twin plane of pigeonite. (long dimension 0.5 mm, Bushveld igneous complex)
General
CategorySilicate mineral (pyroxene)
Formula
(repeating unit)
(Ca,Mg,Fe)(Mg,Fe)Si2O6
Strunz classification9.DA.10
Dana classification65.01.01.04
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 9.7, b = 8.95,
c = 5.24 [Å]; β = 108.59°; Z = 4
Identification
ColorBrown, greenish brown-black
Crystal habitPrismatic crystals, to 1 cm; granular, massive.
TwinningCommonly twinned simply or multiply on {100} or {001}
CleavageGood on {110}, (110) ^ (110) ~87°
FractureConchoidal
TenacityBrittle
Mohs scale hardness6
LusterVitreous to dull
StreakGrey white
DiaphaneitySemitransparent
Specific gravity3.17 - 3.46 measured
Optical propertiesBiaxial (+)
Refractive indexnα = 1.683 - 1.722 nβ = 1.684 - 1.722 nγ = 1.704 - 1.752
Birefringenceδ = 0.021 - 0.030
PleochroismWeak to moderate; X = colorless, pale green, brown; Y = pale brown, pale brownish green, brownish pink; Z = colorless, pale green, pale yellow
2V angle0 - 30° measured
Dispersionweak to distinct
References[1][2][3]

References

  1. ^ http://rruff.geo.arizona.edu/doclib/hom/pigeonite.pdf Handbook of Mineralogy
  2. ^ http://www.webmineral.com/data/Pigeonite.shtml Webmineral data
  3. ^ a b http://www.mindat.org/min-3210.html Mindat.org
  4. ^ Nesse, William (2012). Introduction to Mineralogy (Second ed.). Oxford University Press. p. 300.
  5. ^ Winchell, Alexander N. (1900). "Mineralogical and petrographic study of the gabbroid rocks of Minnesota, and more particularly, of the plagioclasytes". The American Geologist. 26 (4): 197–245.
Augite

Augite is a common rock-forming pyroxene mineral with formula (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6. The crystals are monoclinic and prismatic. Augite has two prominent cleavages, meeting at angles near 90 degrees.

Basalt

Basalt (US: , UK: ) is a mafic extrusive igneous rock formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. More than 90% of all volcanic rock on Earth is basalt. Basalt lava has a low viscosity, due to its low silica content, resulting in rapid lava flows that can spread over great areas before cooling and solidification. Flood basalt describes the formation in a series of lava basalt flows.

Basanite

Basanite ( ) is an igneous, volcanic (extrusive) rock with aphanitic to porphyritic texture.

The mineral assembly is usually abundant feldspathoids (nepheline or leucite), plagioclase, and augite, together with olivine and lesser iron-titanium oxides such as ilmenite and magnetite-ulvospinel; minor alkali feldspar may be present, as illustrated by the position of the field for basanite in the QAPF diagram. Clinopyroxene (augite) and olivine are common as phenocrysts and in the matrix. The augite contains significantly greater titanium, aluminium and sodium than that in typical tholeiitic basalt. Quartz is absent, as are orthopyroxene and pigeonite. Chemically, basanites are mafic. They are low in silica (42 to 45% SiO2) and high in alkalis (3 to 5.5% Na2O and K2O) compared to basalt, which typically contains more SiO2, as evident on the diagram used for TAS classification. Nephelinite is yet richer in Na2O plus K2O compared to SiO2.

Basanites occur both on continents and on ocean islands. Together with basalts, they are produced by hotspot volcanism, for example in the Hawaiian Islands, the Comoros Islands and the Canary Islands.

Bushveld Igneous Complex

The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is approximately 2 billion years old and is divided into four different limbs: the northern, southern, eastern, and western limbs. The Bushveld Complex comprises the Rustenburg Layered suite, the Lebowa Granites and the Rooiberg Felsics, that are overlain by the Karoo sediments. The site was first discovered around 1897 by Gustaaf Molengraaff.Located in South Africa, the BIC contains some of the richest ore deposits on Earth. The complex contains the world's largest reserves of platinum-group metals (PGMs) or platinum group elements (PGEs)—platinum, palladium, osmium, iridium, rhodium, and ruthenium along with vast quantities of iron, tin, chromium, titanium and vanadium. These are used in, but not limited to, jewellery, automobiles and electronics. Gabbro or norite is also quarried from parts of the complex and rendered into dimension stone. There have been more than 20 mine operations. There have been studies of potential uranium deposits. The complex is well known for its chromitite reef deposits, particularly the Merensky reef and the UG-2 reef. It represents about 75 percent of the world's platinum and about 50 percent of the world's palladium resources. In this respect, the Bushveld complex is unique and one of most economically significant mineral deposit complex in the world.

Cobb hotspot

The Cobb hotspot is a marine volcanic hotspot at (46˚ N, 130˚ W), which is 460 km (290 mi) west of Oregon and Washington, North America, in the Pacific Ocean. Over geologic time, the Earth's surface has migrated with respect to the hotspot through plate tectonics, creating the Cobb-Eicklberg seamount chain. The hotspot is currently collocated with the Juan de Fuca Ridge.

Diopside

Diopside is a monoclinic pyroxene mineral with composition MgCaSi2O6. It forms complete solid solution series with hedenbergite (FeCaSi2O6) and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull green crystals in the monoclinic prismatic class. It has two distinct prismatic cleavages at 87 and 93° typical of the pyroxene series. It has a Mohs hardness of six, a Vickers hardness of 7.7 GPa at a load of 0.98 N, and a specific gravity of 3.25 to 3.55. It is transparent to translucent with indices of refraction of nα=1.663–1.699, nβ=1.671–1.705, and nγ=1.693–1.728. The optic angle is 58° to 63°.

Eucrite

Eucrites are achondritic stony meteorites, many of which originate from the surface of the asteroid 4 Vesta and as such are part of the HED meteorite clan. They are the most common achondrite group with well over 100 distinct finds at present.

Eucrites consist of basaltic rock from the crust of 4 Vesta or a similar parent body. They are mostly composed of Ca-poor pyroxene, pigeonite, and Ca-rich plagioclase (anorthite).Based on differences of chemical composition and features of the component crystals, they are subdivided into several groups:

Non-cumulate eucrites Are the most common variety and can be subdivided further:

Main series eucrites formed near the surface and are mostly, though not exclusively, regolith breccias lithified under the pressure of overlying newer deposits.

Stannern trend eucrites are a rare variety.

Nuevo Laredo trend eucrites are thought to come from deeper layers of 4 Vesta's crust, and are a transition group towards the cumulate eucrites.

Cumulate eucrites are rare types with oriented crystals, thought to have solidified in magma chambers deep within Vesta's crust.

Polymict eucrites are regolith breccias consisting of mostly eucrite fragments and less than one part in ten of diogenite, an arbitrary dividing line from the howardites, which are related in structure. They are comparably rare.

Flood basalt

A flood basalt is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Flood basalt provinces such as the Deccan Traps of India are often called traps, after the Swedish word trappa (meaning "stairs"), due to the characteristic stairstep geomorphology of many associated landscapes. Michael R. Rampino and Richard Stothers (1988) cited eleven distinct flood basalt episodes occurring in the past 250 million years, creating large volcanic provinces, lava plateaus, and mountain ranges. However, more have been recognized such as the large Ontong Java Plateau, and the Chilcotin Group, though the latter may be linked to the Columbia River Basalt Group. Large igneous provinces have been connected to five mass extinction events, and may be associated with bolide impacts.

Hisashi Kuno

Hisashi Kuno (久野 久, Kuno Hisashi, 7 January 1910 – 6 August 1969) was professor at the Institute of Geology, University of Tokyo. He was first son of Kamenosuke Kuno (a painter of the Japanese classical school) and Tome Kuno.

List of minerals

This is a list of minerals for which there are articles on Wikipedia.

Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species. Within a mineral species there may be variation in physical properties or minor amounts of impurities that are recognized by mineralogists or wider society as a mineral variety.

Mineral variety names and mineraloids are to be listed after the valid minerals for each letter.

For a complete listing (about 5,000) of all mineral names, see List of minerals (complete).

Mineralogy of Mars

The mineralogy of Mars is the chemical composition of rocks and soil that encompass the surface of Mars. Various orbital crafts have used spectroscopic methods to identify the signature of some minerals. The planetary landers performed concrete chemical analysis of the soil in rocks to further identify and confirm the presence of other minerals. The only samples of Martian rocks that are on Earth are in the form of meteorites. The elemental and atmospheric composition along with planetary conditions is essential in knowing what minerals can be formed from these base parts.

Northwest Africa 7034

Northwest Africa 7034 is a Martian meteorite believed to be the second oldest yet discovered. It is estimated to be two billion years old and contains the most water of any Martian meteorite found on earth. Although it is from Mars it does not fit into any of the three SNC meteorite categories, and forms a new Martian meteorite group named "Martian (basaltic breccia)". Nicknamed "Black Beauty", it was purchased in Morocco and a slice of it was donated to the University of New Mexico by its American owner.

Pigeon Point, Minnesota

Pigeon Point is an isolated peninsula located at the northeast extremity of Minnesota, in Cook County, Minnesota, United States. To the north of the point lies Pigeon Bay, which shares a shoreline with Canada and to the south is Lake Superior. Pigeon Point is the closest mainland U.S. point to Isle Royale, on the far side of the water boundary between Minnesota and Michigan. The extreme end of the point is owned by the United States Coast Guard while the land up to the point is held by the Grand Portage Indian Reservation. The closest town to the point is Grand Portage, Minnesota which lies thirteen miles to the west. There are no roads that lead to this point and is only accessible by boat.

The site is the namesake of the mineral pigeonite.

Pyroxene

The pyroxenes (commonly abbreviated to Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula XY(Si,Al)2O6, where X represents calcium, sodium, iron (II) or magnesium and more rarely zinc, manganese or lithium, and Y represents ions of smaller size, such as chromium, aluminium, iron (III), magnesium, cobalt, manganese, scandium, titanium, vanadium or even iron (II). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a common structure consisting of single chains of silica tetrahedra. Pyroxenes that crystallize in the monoclinic system are known as clinopyroxenes and those that crystallize in the orthorhombic system are known as orthopyroxenes.

The name pyroxene is derived from the Ancient Greek words for fire (πυρ) and stranger (ξένος). Pyroxenes were so named because of their presence in volcanic lavas, where they are sometimes seen as crystals embedded in volcanic glass; it was assumed they were impurities in the glass, hence the name "fire strangers". However, they are simply early-forming minerals that crystallized before the lava erupted.

The upper mantle of Earth is composed mainly of olivine and pyroxene. Pyroxene and feldspar are the major minerals in basalt and gabbro.

Silicate minerals

Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of the Earth's crust.In mineralogy, silica (silicon dioxide) SiO2 is usually considered a silicate mineral. Silica is found in nature as the mineral quartz, and its polymorphs.

On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years. These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis.

Living organisms also contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons ("frustules") from silica extracted from seawater. The frustules of dead diatoms are a major constituent of deep ocean sediment, and of diatomaceous earth.

Suessite

Suessite is a rare iron silicide mineral with chemical formula: Fe3Si. The mineral was named after Professor Hans E. Suess. It was discovered in 1982 during the chemical analysis of The North Haig olivine pigeonite achondrite (ureilite). It is a cream white color in reflected light, and ranges in size from 1 μm "blebs" to elongated grains that can reach up to 0.45 cm in length. This mineral belongs in the isometric crystal class. The isometric class has crystallographic axes that are all the same length and each of the three axes perpendicular to the other two. It is isotropic, has a structural type of DO3 and a crystal lattice of BiF3.

Tholeiitic magma series

The tholeiitic magma series, named after the German municipality of Tholey, is one of two main magma series in igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma into a more evolved, silica rich end member. The International Union of Geological Sciences recommends that tholeiitic basalt be used in preference to the term "tholeiite" (Le Maitre and others, 2002).

Ureilite

Ureilite is a rare type of stony meteorite that has a unique mineralogical composition very different from that of other stony meteorites. This dark grey or brownish meteorite type is named after the village Novy Urey (Cyrillic: Новый Урей), Mordovia Republic of Russia, where a meteorite of this type fell on 4 September 1886. Notable ureilites are the Novo Urei and the Goalpara, also named for the town in which it landed (Goalpara, Assam India). On 7 October 2008, tiny asteroid 2008 TC3 entered Earth's atmosphere and exploded an estimated 37 kilometres (23 mi) above the Nubian Desert in Sudan. Fragments of this asteroid were recovered the following December and were found to be ureilite.

Scientists have discovered amino acids in meteorite 2008 TC3 where none were expected, taking into account high temperatures reached in the explosion of about 1000 °C.

Yamato 691

The Yamato 691 (abbreviated Y-691) is the 4.5 billion year old chondrite meteorite discovered by members of the Japanese Antarctic Research Expedition on the blue ice field of the Queen Fabiola Mountains (Yamato Mountains) in Antarctica, on December 21, 1969.

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