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…

1 août 2010 textures, associated rocks and tectonic environments of anorthosites allow Primordial, Archean and Proterozoic anorthosites are distinctly

the trace of the albite twin lamellae. 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.

Anorthosite texture

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. 5). Anorthosite, type of intrusive igneous rock composed predominantly of calcium-rich plagioclase feldspar.

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 silica mineral.

Anorthosite /ænˈɔːrθəsaɪt/ is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar, with a minimal mafic component. Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present. Anorthosites are of enormous geologic interest, because it is still not fully understood how they form. Most models involve separating plagioclase crystals based on their density.

Anorthosite is by definition an igneous rock consisting of 90-100% plagioclase feldspar. When the amount of mafic minerals exceeds 10 % the name leucogabbro or anorthositic gabbro (alternatively -norite) is commonly used, depending on the nature of the pyroxene.

Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present.

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.
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1 of the KIC. Cumulate textures are relatively widespread on a Lens-shaped aggre- gates of mafic minerals, up to 10 cm in size, commonly appear as well developed corona textures. Primary olivine reacted with plagioclase, with more homogeneous textures. oxydes et apatite peuvent adopter une texture porphyri- place d'un magma enrichi en Fe, Ti et P dans I'anorthosite.

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 silica mineral.
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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.

Such textures have been quantiﬁed in a troctolite–anorthosite from the Proterozoic Lac-St-Jeananorthosite complex,Canada. Crystalsize distributions Anorthosite is typically a coarse-grained intrusive igneous rock with color varies between white, yellowish to brown, shades of gray, blush, and smoky pigment. Tonalite, Diorite, Gabbro, Norite, and Anorthosite These intrusive (plutonic) rocks correspond to fields on diagram 2-2 of Winter.

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Inequigranular anorthosite. Ths rock has a continuum of grain sizes, from very small to quite large. It does not have a phenocrystic texture, having larger crystals set in a much finer-grained matrix. The rock type is anorthosite, a cumulate rock made mostly of plagioclase. Cumulate rocks typically have the same minerals about the same size.

Gabbro and gabbronorite are fine to medium grained, homogeneous and have a mesocumulate texture. granular texture (no relic ophitic texture has been observed). The plagio-clases are inversely zonal with about 75% An in the central zone and with more anorthosite in the peripheral ones. The hornblende is slightly greenish pleocroitic.

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 (e.g., vari-textured gabbro) evidenced by erratic and major changes in

1.2 Color. Black, Bluish - Grey, Brown, Green, Grey, Light Greenish Grey, Pink, White. 1.3 Maintenance.

Most models involve separating plagioclase crystals based on their density. Plagioclase crystals are usually less dense 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 silica Figure 20-1a.