Massive anorthosite has adcumulate texture comprising tightly packed cumulus plagioclase with accessory (<10 vol%) abundances of intercumulus pyroxene and Fe-Ti oxide. The mesocumulate texture that characterizes leucogabbronorite-leuconorite is defined by higher proportions of intercumulus pyroxene and Fe-Ti oxide. TEXTURE • Anorthosite are leucocratic, coarse grained and hypidiomorphic. Some crystals have euhedral form, some have poorly developed faces and others have no crystal form at all. 4. Texture of phases and slip systems Neutron diffraction analysis of a mylonitic anorthosite from the Morin Shear Zone provides quantitative texture data for plagio- clase, clinopyroxene and orthopyroxene (Fig.
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The direction of lamination in the matrix does not wrap around the oikocrysts, as has been observed in other troctolites (compare Sept Iles Intrusion, Higgins, 1991). THE LAC-ST-JEAN ANORTHOSITE Elsewhere on this outcrop other textures are present. 1998-07-01 TEXTURE • Anorthosite are leucocratic, coarse grained and hypidiomorphic. Some crystals have euhedral form, some have poorly developed faces and others have no crystal form at all.
Attempts to subdivide the Lac Rouvray mass into mappable types based on mafic mineral content and total rock textures failed. anorthosite was liquid, not diaplectic and intrudes the basalt (Fig. 1). Although the anorthosite has generally been referred to as a clast in the basalt, the contact of the non-melted anorthosite with the basalt is not in the thin sections and the relationships are obscure.
Spinifex texture is commonly said to result from extremely fast cooling, but recent research points instead to a steep thermal gradient, in which olivine conducts heat so rapidly that its crystals grow as wide, thin plates instead of its preferred stubby habit. osti.gov journal article: lunar anorthosite 15415: texture, mineralogy, and metamorphic history. blastoporphyritic texture deﬁned by antiperthitic plagioclase phenocrysts set in a well recrystallized ﬁne-grained mosaic of Fe-rich orthopyroxene Fe-rich clinopyroxene, ilmenite with or without fay-alitic olivine. The proportion of ferromagnesian minerals increases from anorthosite to ferrodiorite through leuconorites L'anorthosite est une roche ignée intrusive formée de 90% ou plus de feldspath plagioclase et 10% ou moins de minéraux mafiques comme le pyroxène, l'olivine, l'ilménite et la magnétite. L'anorthosite a communément une texture grenue, souvent pegmatitique. Some of the rock at this location remains strong and competent, but much of it has a brittle crumbly or chalky texture as weathering has begun the process of breaking it down into clay. Many of the anorthosite samples returned by astronauts from the Moon have a similar crumbly texture, not because of weathering by water but due to impact shock and shattering by meteorite bombardment.
Typical texture of Archean anorthosite. From the Fiskenæsset. anorthosite (~98% plagioclase). Dixon and Papike. (1975) pictured relict “triple junction” texture between large grains of plagioclase (1 – 3 mm) with small grains .
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The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic textures, developed in fine-grained to medium-grained gabbro and melagabbro layers; (4) size grading, most commonly developed in megacrystic anorthosite layers; (5) "spotted" texture in which pyroxene forms equant crystals that are more resistant to weathering than the plagioclase and, consequently, appear as "spots"; and (6) variable texture Feldspar (in anorthosite) Some varieties of gabbro have few dark minerals, and are made almost entirely of plagioclase feldspar. This rock shows the interlocking texture of the feldspars… The anorthosite highlands of the Moon are primary crust, formed as plagioclase crystallized out of the Moon's initial magma ocean and floated to the top; however, it is unlikely that Earth followed a similar pattern, as the Moon was a water-less system and Earth had water. The Kunene Intrusive Complex (KIC), Namibia, a typical massif-type anorthosite, has not been subjected to a later metamorphic overprint and hence has preserved primary magmatic phases and textures (Ashwal & Twist, 1994; Drüppel et al., 2001, 2007; Mayer et al., 2004). 2591.13 Mottled anorthosite, mottles increasing in size and frequency downwards.
The granoblastic texture (figure 2) is caused by extensive subsolidus recrystallization. Small anhedral grains of plagioclase have smooth boundaries and meet in
Sep 13, 2014 Many lunar meteorites contain anorthositic clasts that may be The texture of the section of Dho 081 we studied (BM2004, M5) is that of a
Winter (2001) An Introduction toIgneous and. Metamorphic Petrology. Prentice Hall. Figure 20-1a. a. Typical texture of Archean anorthosite.
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a. Typical texture of Archean anorthosite. From theFiskenæsset complex, W. Greenland. Myers (1985) Stratigraphy and structure of the Fiskenæsset complex, West Greenland.Grønl. Geol.Unders. Bull 150. Photograph courtesy John Myers.
Thus age, composition and magmatic texture distinguish Proterozoic massif-type from Archean megacrystic anorthosites. Aside from anorthosite, the dominant rock types of anorthosites massif, include leucogabbro, leuconorite and leucotroctolite, with minor gabbroic rocks. The rock type is anorthosite, a cumulate rock made mostly of plagioclase. Cumulate rocks typically have the same minerals about the same size. In this case, grain textures look somewhat annealed, possibly because of deformation and annealing when it was still very hot. Stillwater Complex, Montana.
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Bull 150. Photograph courtesy John Myers. Winter (2001) An Introduction toIgneous and Metamorphic Petrology. Prentice Hall. Figure 20-2 Get detailed information about Wehrlite vs Anorthosite texture, color, appearance Get detailed information about Sandstone vs Anorthosite texture, color, appearance Get detailed information about Marl vs Anorthosite texture, color, appearance Anorthosite is a white to light gray-colored intrusive igneous rock. Major minerals of anorthosite include just feldspar. Anorthosite has a coarse-grained texture due to slow cooling underground.
Typical samples sizes are generally 1-2 inches in length or width but can vary based on availability and natural formation. Abstract. Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a The dominant texture is ‘Nodular’ troctolite, in which amoeboid olivine oikocrysts 10–20 cm in diameter are spaced 20–30 cm apart within a matrix of anorthosite ( Woussen et al., 1988; Figs 1 and 2 ). The oikocrysts consist of a single or possibly a few olivine crystals with abundant chadocrysts of plagioclase. Both plagioclase and olivine are 5–10 mm long. The Layered Troctolite terminates abruptly along sinuous boundaries against Massive Anorthosite, which has a texture similar to anorthositic patches in both types of troctolite. Massive anorthosite Olivine oikocrysts - plagioclase chadocryst orientations indicated schematically where visible 20 cm Fig. 2.
Texture of Gneiss is Banded, Foliated, Platy whereas that of Anorthosite is Foliated, Glassy. Based on the texture of rocks, they are used for various purposes. Quantitative texture analysis of an anorthite (polycrystalline plagioclase feldspar) has been under takenusinganoptical microscopeequippedwithauniversal stage. Themicrostructurewasstudiedon three orthogonal sections. The microstructural shape analysis suggests an axial fabric which is confirmedbytexture analysis.