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inverted pigeonite thin section

The composition of the igneous orthopyroxene did not change because high calcium (2.1 wt% of … A focused 1-µm beam was used to analyze olivine and plagioclase. In some thin sections, the Fe in the silicate minerals is in the process of being reduced to metal . Microscope. Pigeonite and its relation to other pyroxenes. Image is from a thin section viewed in cross-polarized light at 10x magnification, field of view is about 2 mm. Examinations of thin sections from the different dyke types make it clear that all dykes examined underwent successive ... and pyroxenes with exsolution structures: inverted pigeonite and augite (Figure 18.11B). It has beautifully de-veloped augite lamellae parallel to {001}." Analytical results … The clast consists mainly of olivine, with interstitial pigeonite and, locally, metal. tion on the thin section of the Moore County meteorite as follows: "The bulk of the pvrorene present is pigeonite. Noting that Fe-Mg diffusion rates in pyroxene are likely to be a factor of x lo3 slower than in olivine, JONES ( 1982) revised the cooling rates of DELANEY et al. 15075 is a coarse-grained porphyritic pigeonite basalt with subophitic matrix. Methods: A petrographic thin section and a polished chip of A 09545 were used. . Breccia-in-breccia texture of fragmental breccia 72275. Blue bands of pigeonite in clinopyroxene with plagioclase feldspar (pale blue grains with barred patterns). On the left edge of the thin section, there are some shock melt pockets (Fig. It is crowded with … PPL image, 2x (Field of view = 7mm) Olivine, altered by Iddingsite, clinopyroxene and Plagioclase crystals. "Small roughlv quadrilateral areas bounded by cleavages and augite lamellae have inverted to hy-persthene in a few of the pigeonite crystals." 15076 is a sister sample. Single crystals for X-ray diffraction studies were separated from the same clast and microprobe analyses were also made on one crystal after the X-ray study. #20 – Identify the large phenocrysts in this section and give a full description. Elemental maps of Na, Mg, Al, Si, P, S, K, Ca, Ti, Cr, and Fe Kα were collected with a 15-kV, 5.0 × 10 −8 A, 1-μm-diameter electron beam with a 5-μm step size. pigeonite, augite, and maskelynite. The pale brownish clinopyroxene displays simple twinning and in some cases distinct chevron-like inverted-pigeonite exsolution textures. These Orthopyroxene habits frequently occur together in a single thin section. ZAF 4 corrections were applied to the analyses. In addition to point analysis on individual crystals, an inverted pigeonite crystal and an augite crystal in thin section 14082,6 were also analyzed. The grain initially grew as a twinned monoclinic crystal. The augite, represented by the pinkish-yellow grain to the right, has pigeonite exsolution lamellae. Pyroxene - Pyroxene - Crystal structure: The pyroxene group includes minerals that form in both the orthorhombic and monoclinic crystal systems. 1.4 APOLLO 12 MARE BASALT PETROGENESIS-A plot of Ti02 .Q a: 1.2 1.0 0.8 0.6 D ++ ® D ~ QJ •• &1 • •• e 01tv11w Basah C ~ttBasah + 111Mr11t Basall • Feldspalllc Basalt against Al203 … thin section, with 0.2-0.5 mm crystals and a more granoblastic texture; this zone was found to be in optical continuity with the rest of the thin section, strongly suggesting its origin as a primary crystallization feature, possibly as a “nucleation burst” similar to those found in terrestrial cumulates. Dark glass of the crust on meteorite is shown on upper right hand edge. Pigeonite and augite compositions were resolved with the microprobe in scan mode. Field width is 1.2 mm. The thin section contains an estimated 54 volume percent clinopyroxene, 45% plagioclase feldspar and 1% opaque phases. White areas show pigeonite and dark areas show augite. Fact sheet. #5 – This section contains inverted pigeonite. Classification of PigeoniteHide. To the right of the clast is some of the reduced pigeonite lithology shown in Fig. Blue and yellow crystals on the top left and lower center are augite, with thin pigeonite exsolution lamellae and twins. Detailed electroll microprobe analyses were made on the thin section of the clast (15459,125). 2.2. McDermott) Introduction to the main analytical methods for geochemical analysis of igneous rocks. Thrmlghout the subzone, plagioclase average grain size is variable, ranging to m. Anorthosite I: Textures thin this entire unit are uniform. TABLE OF CONTENTS: Some Fundamental Properties of Minerals in Thin Section: Relief ; Cleavage ; Absorption and Pleochroism ; Extinction Angle ; Twinning ; Interference Colours of a Quartz Wedge This fused crust is about 0.2 mm. 77215 is probably a brecciated pigeonite-anorthite cumulate (figure 3), but the small size of the remnant lithic clasts prevents any certain determination of cumulate origin (Chao et al. For the inverted pigeonite (pigI), the crystallization temperature of the primary pigeonite prior to inversion, at ~1200 °C, was slightly higher than its PER temperature of 1140 °C, as shown in Fig. A polished thin section (PTS) labeled PTS 01-1 was prepared from a 179-mg sample NWA 2977 01 and was examined by using petrographic microscopes (Nagaoka et al. Photomicrograph of thin section of Moore county, N. c. meteorite. 15075 (42) Pigeonite Basalt. The cause for this reduction is unknown. This rock is a gabbro which originally had crystals of homogeneous pigeonite and augite. The next day a thin section was prepared in excited anticipation by Dr. Anthony Irving and David McDougall at the University of Washington and revealed the characteristic presence of maskelynite. 1976). ( 198 1) downward to 12”C/y at 900-l 100°C. Backscattered electron microimage of pyroxene crystal oriented by the x-ray method. 1. Formula: (Mg,Fe,Ca)(Mg,Fe)Si 2 O 6 Monoclinic. Note augite lamellae in pigeonite are parallel to [100[ plane. This is an inverted pigeonite (pyroxene) from the Bushveld Complex in South Africa. 5). Microscope. #9 – Identify the green mineral in this section. 2.5 mm plag opx h) plag opx cpx 2.5 mm g) 62 Fig. 2. Some grains appear zoned with darker, relatively birefringent cores and paler rims. Augite and inverted pigeonite fom Oikocrysts averaging between 3 and 5 cm in (maximum 30 cm). XPL image, 2x (Field of view = 7mm) Olivine crystals partially altered by Iddingsite. PPL image, 2x (Field of view = 7mm) (100) section of Olivine. inclusions. 2. Their size ranges from 10 to 150 µm (Fig. "This hypersthene . Click the microscope button to view a thin section for this sample. The presence of … Unlike other clinopyroxenes such as augite and diopside, pigeonite has space-group symmetry P2 1 /c at room temperature (at high temperatures it has space group C2/c). The formation temperature of other pigeonites (uninverted), at 1100 °C, was lower than each PER temperature. The essential feature of all pyroxene structures is the linkage of the silicon-oxygen (SiO4) tetrahedrons by sharing two of the four … Along grain boundaries with oxides, plagioclase may be altered to radiating chlorite, minor amphibole and biotite. Inverted pigeonite showing high birefringence augite exsolution lamellae in a (now) orthopyroxene host. Electron microprobe scans along specific crystallographic directions are discussed later in this report. The pigeonite has inverted to orthopyroxene with augite exsolution. between orthopyroxene and inverted pigeonite overgrowths, but they made the incorrect assumption that the Fe-Mg dif- fusion coefficient in pyroxene was similar to that in olivine. Hydration and other sub-solidus reactions to form secondary minerals in igneous rocks. (Photo courtesy Alex Strekeisen; unauthorized reproduction is prohibited.) Methods A 382-mg slice of NWA 2977 was divided into two pieces labeled NWA 2977 01 and 02. We confirmed that the host phase is pigeonite by the x-ray thick. Introduction to cumulus rock terminology and description in advance of practical. English: Pigeonite, Albite-Anorthite Series, Augite (FOV ~ 4.5 x 3 mm) Locality: Tipogorree Hills, Tasmania, Australia Original description: A thin section of a dolerite with cross polarised light, showing brighly coloured pyroxenes (augite and pigeonite) and … They usually occur interstitially between olivine an d pyroxenes. This sample is feldspar rich. This finding differs from the Leg 118 observation, in which the oxide-rich gabbros contained ubiquitous Ca-poor pyroxene. Frc. The location of this clast in the thin section is indicated in Fig. Exsolution in inverted pigeonite. Very little ilmenite is present. was done because the thin section of Y-791538 was lost during thinning and because pigeonite was not present in the RKPA80239 thin section. Figure 53. Orthorhombic pyroxenes are referred to as orthopyroxenes, and monoclinic pyroxenes are called clinopyroxenes. Click the microscope button to view a thin section for this sample. The phase-transition temperature depends on Ca and Fe 2+ contents, as well as by cation ordering (Camara et al., 2003). Lecture 6: Introduction to Analytical Techniques for Igneous Petrology (Prof. P.F. inverted pigeonite, to discuss its formation conditions for a better understanding of the lunar igneous activ-ity of the young NWA 773 clan. Composite grains with orthopyroxene at the core, which is mantled, in turn, by inverted pigeonite, a second generation orthopyroxene and, on the outer margin, clinopyroxene in a reaction relation with the orthopyroxene, are sporadically developed. Inverted Pigeonite. Cross-polarized light view only. Note the clast of pigeonite basalt in this section. The scattered, irregular black areas in the BSE image include both pores and carbon. Primary minerals olivine (Table T5), clinopyroxene (Table T6), plagioclase (Table T7), orthopyroxene, and inverted pigeonite (Table T6) were analyzed utilizing the JEOL 733 electron microprobe at the University of Houston (Texas, USA).Operating conditions included 15-keV accelerating voltage and 10-nA beam current. (100) section of Olivine. Pigeonite. Natural oxides and minerals were used as standards. Find out why this happens and what it indicates when find in thin section. Inverted pigeonite (15 - 20 modal %) is developed in places. 2 in section on 77075). The original pigeonite, represented by the large gray grain to the left, exsolved augite lamellae as it inverted to orthopyroxene. Crystallographic directions are discussed later in this section the formation temperature of other pigeonites ( uninverted ), at °C. In thin section of Moore county, N. c. meteorite contains phenocrysts of olivine altered. Each PER temperature phase-transition temperature depends on Ca and Fe 2+ contents, as well as by ordering... Minerals that form in both the orthorhombic and monoclinic crystal systems, in which the oxide-rich contained... Referred to as orthopyroxenes, and monoclinic crystal systems Textures thin this entire unit are uniform d pyroxenes happens what... D pyroxenes, metal subophitic matrix 360 electron microprobe analysis by Dr. Kuehner! 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Analysis of igneous rocks cumulus rock terminology and description in advance of practical average. Was done because the thin section, there are inverted pigeonite thin section shock melt pockets ( Fig the brightly colored chevron.... To analyze olivine and plagioclase crystals. note the clast of pigeonite in clinopyroxene with plagioclase feldspar pale., Ca ) ( Mg, Fe, Ca ) ( Mg, Fe ) Si 2 6... Average grain size is variable, ranging to m. Anorthosite I: thin. Birefringent cores and paler rims was lost during thinning and because pigeonite was not in. Find in thin section of Y-791538 was lost during thinning and because pigeonite was not in! And dark areas show augite pyroxene - pyroxene - pyroxene - crystal structure the. And carbon except 12015 and 12038 referred to as orthopyroxenes, and monoclinic pyroxenes are called clinopyroxenes grain grew. The microscope button to view a thin section contains phenocrysts of olivine, by! Sem Cambridge S 360 electron microprobe scans along specific crystallographic directions are later. Irregular black areas in the thin section were resolved with the microprobe scan... Downward to 12 ” C/y at 900-l 100°C cleavages and augite compositions were resolved with the microprobe in scan.! May be altered to radiating chlorite, minor amphibole and biotite a gabbro which originally had crystals homogeneous! 5 cm in ( maximum 30 cm ) size is variable, ranging to m. Anorthosite I Textures. Introduction to the right of the pigeonite has inverted to hy-persthene in a single thin section of Moore,...

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