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Dorrel Rock
Dorrel Rock () is a nunatak located southwest of the summit of Mount Murphy, protruding through the ice near the head of Pope Glacier, on the Walgreen Coast, Marie Byrd Land. It was mapped by the United States Geological Survey from surveys and U.S. Navy air photos, 1959–66, and was named by the Advisory Committee on Antarctic Names after Leo E. Dorrel, U.S. Navy, a hospital corpsman with the Byrd Station winter party, 1966.Stewart, J., 2011. ''Antarctica: An Encyclopedia,'' 2nd ed. Jefferson, North Carolina and London, McFarland & Company, Inc. 1771 pp. Dorrel Rock is an in diameter exposure of gabbro cut by dikes of benmoreite and trachyte. Dorrel Rock is a unique exposure of intrusive Cenozoic igneous rocks within Marie Byrd Land. The gabbro is coarse-grained and composed of labradorite, diopside and ilmenite, with minor titanomagnetite, kaersutite, biotite, and amphibole. The benmoreite dikes consist largely of sodic oligoclase, hastingsite-ferropargasite, scar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nunatak
A nunatak (from Inuit ''nunataq'') is the summit or ridge of a mountain that protrudes from an ice field or glacier that otherwise covers most of the mountain or ridge. They are also called glacial islands. Examples are natural pyramidal peaks. When rounded by glacial action, smaller rock promontories may be referred to as rognons. The word is of Greenlandic origin and has been used in English since the 1870s. Description The term is typically used in areas where a permanent ice sheet is present and the nunataks protrude above the sheet.J. J. Zeeberg, ''Climate and Glacial History of the Novaya Zemlya Archipelago, Russian Arctic''. pp. 82–84 Nunataks present readily identifiable landmark reference points in glaciers or ice caps and are often named. While some nunataks are isolated, sometimes they form dense clusters, such as Queen Louise Land in Greenland. Nunataks are generally angular and jagged, which hampers the formation of glacial ice on their tops, although snow can a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ilmenite
Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing inks, fabrics, plastics, paper, sunscreen, food and cosmetics. Structure and properties Ilmenite is a heavy (specific gravity 4.7), moderately hard (Mohs hardness 5.6 to 6), opaque black mineral with a submetallic luster. It is almost always massive, with thick tabular crystals being quite rare. It shows no discernible cleavage, breaking instead with a conchoidal to uneven fracture. Ilmenite crystallizes in the trigonal system with space group ''R''. The ilmenite crystal structure consists of an ordered derivative of the corundum structure; in corundum all cations are identical but in ilmenite Fe2+ and Ti4+ ions occupy alternating layers perpendicular to the trigonal c axis. Pure ilmenite is paramagnetic (showing only very weak attrac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sanidine
Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi3O8). Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures. At yet lower temperatures, microcline, a triclinic polymorph of potassium feldspar, is stable. Due to the high temperature and rapid quenching, sanidine can contain more sodium in its structure than the two polymorphs that equilibrated at lower temperatures. Sanidine and high albite constitute a solid solution series with intermediate compositions termed anorthoclase. Exsolution of an albite phase does occur; resulting cryptoperthite can best be observed in electron microprobe images. Occurrence In addition to its presence in the groundmass of felsic rocks, sanidine is a common phenocryst in rhyolites and, to a lesser extent, rhyodacites. Trachyte consists largely of fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hedenbergite
Hedenbergite, Ca Fe Si2 O6, is the iron rich end member of the pyroxene group having a monoclinic crystal system. The mineral is extremely rarely found as a pure substance, and usually has to be synthesized in a lab. It was named in 1819 after M.A. Ludwig Hedenberg, who was the first to define hedenbergite as a mineral. Contact metamorphic rocks high in iron are the primary geologic setting for hedenbergite. This mineral is unique because it can be found in chondrites and skarns ( calc–silicate metamorphic rocks). Since it is a member of the pyroxene family, there is a great deal of interest in its importance to general geologic processes. Properties Hedenbergite has a number of specific properties. Its hardness is usually between five and six with two cleavage plains and conchoidal fracture. Color varies between black, greenish black, and dark brown with a resinous luster. Hedenbergite is a part of a pyroxene solid solution chain consisting of diopside and augite, and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Groundmass
The matrix or groundmass of a rock is the finer-grained mass of material in which larger grains, crystals, or clasts are embedded. The matrix of an igneous rock consists of finer-grained, often microscopic, crystals in which larger crystals, called phenocrysts, are embedded. This porphyritic texture is indicative of multi-stage cooling of magma. For example, porphyritic andesite will have large phenocrysts of plagioclase in a fine-grained matrix. Also in South Africa, diamonds are often mined from a matrix of weathered clay-like rock (kimberlite) called "yellow ground". The matrix of sedimentary rocks is finer-grained sedimentary material, such as clay or silt, in which larger grains or clasts are embedded. It is also used to describe the rock material in which a fossil is embedded. Cementation All sediments are at first in an incoherent condition (e.g. sands, clays and gravels, beds of shells), and they may remain in this state for an indefinite period. Millions of years have ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microphenocryst
image:montblanc granite phenocrysts.JPG, 300px, Granites often have large feldspar, feldspathic phenocrysts. This granite, from the Switzerland, Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter 2.3 cm) for scale. A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock Matrix (geology), groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called Porphyry (geology), porphyries, and the adjective porphyritic is used to describe them. Phenocrysts often have euhedral forms, either due to early growth within a magma, or by post-emplacement recrystallization (geology), recrystallization. Normally the term ''phenocryst'' is not used unless the crystals are directly observable, which is sometimes stated as greater than .5 millimeter in di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldspars and the ''alkali'' (potassium-sodium) feldspars. Feldspars make up about 60% of the Earth's crust, and 41% of the Earth's continental crust by weight. Feldspars crystalize from magma as both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rocks. Compositions The feldspar group of minerals consists of tectosilicates, silicate minerals in which silicon ions are linked by shared oxygen ions to form a three-dimensional network. Compositions of major elements in common feldspars can be expressed in terms of three endmembers: * potassium feldspar (K-spar) ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phenocryst
300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter 2.3 cm) for scale. A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them. Phenocrysts often have euhedral forms, either due to early growth within a magma, or by post-emplacement recrystallization. Normally the term ''phenocryst'' is not used unless the crystals are directly observable, which is sometimes stated as greater than .5 millimeter in diameter. Phenocrysts below this level, but still larger than the groundmass crystals, are termed ''microphenocrysts''. Very large phenocrysts a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Euhedral
Euhedral crystals (also known as idiomorphic or automorphic crystals) are those that are well-formed, with sharp, easily recognised faces. The opposite is anhedral (also known as ''xenomorphic'' or ''allotriomorphic''): a rock with an anhedral texture is composed of mineral grains that have no well-formed crystal faces or cross-section shape in thin section. Anhedral crystal growth occurs in a competitive environment with no free space for the formation of crystal faces. An intermediate texture with some crystal face-formation is termed subhedral. Crystals that grow from cooling liquid magma typically do not form smooth faces or sharp crystal outlines. As magma cools, the crystals grow and eventually touch each other, preventing crystal faces from forming properly or at all. When snowflakes crystallize, they do not touch each other. Thus, snowflakes form euhedral, six-sided twinned crystals. In rocks, the presence of euhedral crystals may signify that they formed early in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism. Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. Small grains of magnetite are very common in igneous and metamorphic rocks. The chemical IUPAC name is iron(II,III) oxide and the common chemical name is ''ferrous-ferric oxide''. Properties In addition to igneous rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake and marine sediments ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oligoclase
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite ( Na Al Si3 O8) and anorthite ( CaAl2Si2O8). The albite:anorthite molar ratio of oligoclase ranges from 90:10 to 70:30. Oligoclase is a high sodium feldspar crystallizing in the triclinic system. The Mohs hardness is 6 to 6.5 and the specific gravity is 2.64 to 2.66. The refractive indices are: nα=1.533–1.543, nβ=1.537–1.548, and nγ=1.542–1.552. In color it is usually white, with shades of grey, green, or red. Oligoclase is a common mineral in the more silica-rich varieties of igneous rock and in many metamorphic rocks. Name and discovery The name oligoclase was given by August Breithaupt in 1826 from the grc, όλίγος, oligos, little, and grc, κλᾶν, klân, to break, because the mineral was thought to have a less perfect cleavage than albite. It had previously been recognize ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amphibole
Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is Amp. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups. Mineralogy Amphiboles crystallize into two crystal systems, monoclinic and orthorhombic. In chemical composition and general characteristics they are similar to the pyroxenes. The chief differences from pyroxenes are that (i) amphiboles contain essential hydroxyl (OH) or halogen (F, Cl) and (ii) the basic structure is a double chain of tetrahedra (as opposed to the single chain structure of pyroxene). Most apparent, in hand specimens, is that amphiboles form oblique cleavage planes (at around 120 degrees), whe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
