Augite
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Augite is a solid solution in the pyroxene group. Diopside and hedenbergite are important endmembers in augite, but augite can also contain significant aluminium, titanium, and sodium and other elements. The calcium content of augite is limited by a miscibility gap between it and pigeonite and orthopyroxene: when occurring with either of these other pyroxenes, the calcium content of augite is a function of temperature and pressure, but mostly of temperature, and so can be useful in reconstructing temperature histories of rocks. With declining temperature, augite may exsolve lamellae of pigeonite and/or orthopyroxene. There is also a miscibility gap between augite and omphacite, but this gap occurs at higher temperatures. There are no industrial or economic uses for this mineral.[5][6]
Occasional specimens have a shiny appearance that give rise to the mineral's name, which is from the Greek augites, meaning \"brightness\", although ordinary specimens have a dull (dark green, brown or black) luster. It was named by Abraham Gottlob Werner in 1792.[3]
Augite is the most common pyroxene mineral and a member of the clinopyroxene group. Some people use the names \"augite\" and \"pyroxene\" interchangeably, but this usage is strongly discouraged. There are a large number of pyroxene minerals, many of which are distinctly different and easy to identify. Augite, diopside, jadeite, spodumene, and hypersthene are just a few of the distinctly different pyroxene minerals.
Light reflecting from cleavage surfaces and crystal faces of augite produces a vitreous luster, while light striking other surfaces produces a dull luster. Augite has a Mohs hardness of 5.5 to 6. Its specific gravity of 3.2 to 3.6 is higher than most other minerals in the rocks in which it occurs.
Augite does not have any physical, optical, or chemical properties that make it especially useful. It is therefore one of the few minerals that has no commercial use. The calcium content of augite has been found to be of limited use in studies of the temperature history of igneous rocks.
Augite is most easily confused with hornblende. Hornblende has highly reflective cleavages whereas augite cleavages are dull. Hornblende tends to form elongate rectangular crystals whereas augite crystals tend to be blocky. Finally, if you can find two intersecting cleavage planes, hornblende cleavages always intersect at 60 or 120 whereas augite cleavages always intersect at about 90.
Augite is the most common pyroxene in the earth's crust. It is an essential constituent of basic magmatic rocks (andesites, basalts, gabbros, etc...) and ultrabasic (pyroxenites, etc...), which one also meets in metamorphic rocks of high temperature (granulite) and of contact. Its name comes from the Greek auge (shiny), alluding to the appearance of its cleavage surfaces. The chemistry of augite is complex : it forms a continuous series with diopside and hedenbergite, by replacing atoms of silicon and magnesium by atoms of aluminum ; in addition, the presence of titanium and chromium is frequent, especially in volcanic environments. The assimilation of sodium also allows the formation of terms of passage towards aegyrine : these are the aegyrinic augites. A frequent phenomenon is the alteration of augite to green hornblende (\"ouralitization\"). Well crystallized, augite shows crystals with various facies, elongated or squat with square or octagonal section, frequently twinned (main photo). Its color is black with brownish to greenish reflections. It is a mineral that has no particular use.
In France, the volcanoes of the Massif Central have yielded superb individuals : 6 cm in Mézenc (Haute-Loire), more than 3 cm in Cantal and Ardèche. In Puy-de-Dôme, augite is very abundant in the pozzolana of Puy de Corent (photo on the right), although automorphic crystals are rare. It is found in alluvium of volcanic products from the Chaîne des Puys, at Aydat for example in 5 mm perfect and twinned crystals.
Single or multiple twins on {100} (in bishop's bonnet) and more rarely on {001} are known. In addition, orthopyroxenes such as enstatite may exhibit clinopyroxene exsolutions (augite) just as augite may exhibit orthopyroxene exsolutions. These oriented exsolutions are often confused with twins.
Augite andesite igneous rock specimens from Thirlmere, Cumbria, UK which are of late Ordovician age which form part of the Barrowdale volcanic group. The samples are of intermediate composition and contain phenocrysts of the pyroxene mineral, augite, giving the normally dark blue rock a black speckled appearance. The samples are available in 3 sizes and come supplied in a card tray with a label.
Augite andesite is a variant of the fine grained igneous rock, andesite which contains coarse grained phenocrysts of augite crystals. An extrusive rock of intermediate composition, containing between 50 to 63% of silica, the samples have a dark colour with a blue tint while the augite crystals provide a speckled black appearance. The rock is estimated to have formed during the late Ordovician period and forms part of the Barrowdale volcanic group with other rocks such as dacite and basalt also being present in the area as part of a pre-caldera formation. The rock is slightly denser than our regular line of andesite due to the added pyroxene crystals of augite as phenocrysts. Ideal for established collections and higher level education to exhibit the presence of phenocrysts in igneous material, the rock samples come from Thirlmere, Cumbria, UK and are available in 3 sizes and come supplied in a card tray with a label.
Hypersthene - is commonly found in both plutonic and volcanic igneous rocks and in meta-igneous rocks as well. It is distinguished from augite by its lower interference colors and lack of inclined extinction relative to {110}. Hypersthene is sometimes pleochroic, showing light pink to light green colors. The chemical composition of hypersthene can be estimated using 2V (see p. 163 of DHZ). Compositions close to Enstatite are optically positive with a 2V of 60 to 90o, whereas intermediate compositions are optically negative with a 2V of 50 to 90o.
Pigeonite - is generally only found in volcanic igneous rocks, although, as mentioned above, it can occur as exsolution lamellae in augites of more slowly cooled igneous rocks. Pigeonite is distinguished from augite by its lower 2V of 0 to 30o, and is distinguished from hypersthene by its lack of pleochroism, lower 2V and inclined extinction relative to the {110} cleavage.
A shiny, dark-green to black Pyroxene mineral. Augite is a translucent, silicate mineral containing large amounts of Magnesium, Iron, and Aluminum. It occurs throughout the world, often in association with Basalt or Gabbro. In North America, augite is found in Colorado, Oregon, New York, and Ontario. Augite is also found in lunar rocks and meteorites.
Love how dark those are. I would have thought at first glance they were the very dark garnets that are found in Connecticut. I was unfamiliar with augite as well. Thank you for sharing these outcrop locales. The number of places to go rockhounding is not increasing alas.
Since the introduction1 to geochemistry of crystallization theories developed in metallurgy, it has been thought that the effects of kinetic parmeters such as the rate of crystal growth and the rate of diffusive transport of elements in the melt could significantly affect the partition of trace elements between mineral and magma. This conclusion has not, however, been demonstrated unequivocally, mainly because the extent of variations of equilibrium partition coefficients with T, P and chemistry is not well known. Henderson and Williams2 found a correlation between morphology and apparent partition coefficient of uranium between olivine and basaltic melt. Data on diffusivity of elements (see ref. 3) and on crystal growth kinetics together with the development of secondary ion mass spectrometry (SIMS) techniques, enable crystal zoning to be studied with respect to trace elements and the kinetic effects to be evaluated quantitatively. Trace element zoning (or lack of it) of minerals is important, as many kinetic-based crystallization models predict trace element zoning in crystals. This letter presents trace element data on a sector-zoned augite phenocryst based on the ion-probe spot analyses. The fact that the slower-growing prism sector [100] is enriched in both compatible and incompatible elements relative to the faster-growing basal sector [1Ì„11] strongly supports Dowty's4 model for crystal growth involving preferential adsorption of elements onto growing crystal faces in proportion to the charge/size ratio of the elements.
Augite is a mineral. The mineral's name comes from the Greek word augites, meaning \"brightness\". However, augites only look shiny some of the time. Most augites have a dull (dark green, brown or black) color.Augite is a pyroxene.
Augite occurs in range of colors from black to dark brown, light brown, green and brown green. It has translucent to opaque appearance with prominent cleavages, vitreous luster and greenish gray streak. It is non-fluorescent and forms massive fibers, granules or columns. Its fractures are brittle producing small, conchoidal fragments. The hardness of augite ranges from 5 to 6.5, and its average density is 3.4 g/cm3.
Composition Clinopyroxenes have general formula (Ca,Mg,Fe,Na)(Mg,Fe,Al)(Si,Al)2O6. Most clinopyroxenes in igneous and metamorphic rocks (generally termed augite) can be thought of as (Ca,Mg,Fe)2Si2O6, with small amounts of Al, Mn and Na substituting for other elements. The most significant clinopyroxene end member is diopside, CaMgSi2O6. Its Fe equivalent, CaFeSi2O6 is termed hedenbergite. Near end-member diopside is found in some marbles. Diopside and hedenbergite are the most dominant components in most augite. 59ce067264