inverted pigeonite thin section

Blue bands of pigeonite in clinopyroxene with plagioclase feldspar (pale blue grains with barred patterns). 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. Their size ranges from 10 to 150 µm (Fig. Microscope. To the right of the clast is some of the reduced pigeonite lithology shown in Fig. The thin section contains an estimated 54 volume percent clinopyroxene, 45% plagioclase feldspar and 1% opaque phases. 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. 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 Microprobe analyses were determined using a SEM Cambridge S 360 electron microprobe equipped with EDS Link Analytical QX 2000. 15076 is a sister sample. The presence of … On the left edge of the thin section, there are some shock melt pockets (Fig. Classification of PigeoniteHide. "Small roughlv quadrilateral areas bounded by cleavages and augite lamellae have inverted to hy-persthene in a few of the pigeonite crystals." 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 … Exsolution in inverted pigeonite. Clive R. Neal and ... grained Study of corresponding thin sections demonstrate heterogeneities in all except 12015 and 12038. Detailed electroll microprobe analyses were made on the thin section of the clast (15459,125). Orthorhombic pyroxenes are referred to as orthopyroxenes, and monoclinic pyroxenes are called clinopyroxenes. 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). Microscope. inverted pigeonite, to discuss its formation conditions for a better understanding of the lunar igneous activ-ity of the young NWA 773 clan. Backscattered electron microimage of pyroxene crystal oriented by the x-ray method. The phase-transition temperature depends on Ca and Fe 2+ contents, as well as by cation ordering (Camara et al., 2003). 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. It has beautifully de-veloped augite lamellae parallel to {001}." This finding differs from the Leg 118 observation, in which the oxide-rich gabbros contained ubiquitous Ca-poor pyroxene. 15075 (42) Pigeonite Basalt. XPL image, 2x (Field of view = 7mm) Olivine crystals partially altered by Iddingsite. 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. The scattered, irregular black areas in the BSE image include both pores and carbon. Scanning electron microscopy (SEM) was performed with a FEI Inspect S50 instrument, equipped with an energy-dispersive spectrometry (EDS) detector, at the Royal Belgian Institute of Natural Science, and with awith a JEOL 6400 at the Vrije Universiteit Brussel, Brussels, Belgium. Inverted pigeonite showing high birefringence augite exsolution lamellae in a (now) orthopyroxene host. Along grain boundaries with oxides, plagioclase may be altered to radiating chlorite, minor amphibole and biotite. Field width is 1.2 mm. Electron microprobe scans along specific crystallographic directions are discussed later in this report. Note the clast of pigeonite basalt in this section. 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. Methods A 382-mg slice of NWA 2977 was divided into two pieces labeled NWA 2977 01 and 02. 2.2. A thin section-scale backscattered electron (BSE) image and X-ray elemental maps were obtained by using a JEOL JXA-8900 electron probe microanalyzer (EPMA) at Waseda University. Image is from a thin section viewed in cross-polarized light at 10x magnification, field of view is about 2 mm. Pyroxene - Pyroxene - Crystal structure: The pyroxene group includes minerals that form in both the orthorhombic and monoclinic crystal systems. Find out why this happens and what it indicates when find in thin section. Full confirmation required expert electron microprobe analysis by Dr. Scott Kuehner. The original pigeonite, represented by the large gray grain to the left, exsolved augite lamellae as it inverted to orthopyroxene. Cross-polarized light view only. Figure 52. This rock is a gabbro which originally had crystals of homogeneous pigeonite and augite. Pigeonite and its relation to other pyroxenes. The location of this clast in the thin section is indicated in Fig. Hydration and other sub-solidus reactions to form secondary minerals in igneous rocks. (100) section of Olivine. K-5a – This section contains phenocrysts of olivine, plagioclase and pyroxene. We confirmed that the host phase is pigeonite by the x-ray thick. Click the microscope button to view a thin section for this sample. #5 – This section contains inverted pigeonite. Fact sheet. 2. The two twins then exsolved calcic pyroxene on (0 0 1) which formed the brightly colored chevron pattern. In some thin sections, the Fe in the silicate minerals is in the process of being reduced to metal . Pigeonite is totally lacking in the thin sections of Leg 179 gabbros we examined, and orthopyroxene is present in only four out of 20 oxide-rich samples. tion on the thin section of the Moore County meteorite as follows: "The bulk of the pvrorene present is pigeonite. #9 – Identify the green mineral in this section. 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. 2 in section on 77075). Maximum pyroxene grain size is 2.2x1.0 mm. Phosphates (mainly merrillite) are widespread in these areas. Breccia-in-breccia texture of fragmental breccia 72275. ( 198 1) downward to 12”C/y at 900-l 100°C. Dark glass of the crust on meteorite is shown on upper right hand edge. Very little ilmenite is present. 4). 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. 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). pigeonite, augite, and maskelynite. The essential feature of all pyroxene structures is the linkage of the silicon-oxygen (SiO4) tetrahedrons by sharing two of the four … 1. These Orthopyroxene habits frequently occur together in a single thin section. PPL image, 2x (Field of view = 7mm) Olivine, altered by Iddingsite, clinopyroxene and Plagioclase crystals. . This is an inverted pigeonite (pyroxene) from the Bushveld Complex in South Africa. 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. This fused crust is about 0.2 mm. "This hypersthene . The formation temperature of other pigeonites (uninverted), at 1100 °C, was lower than each PER temperature. Figure 53. They usually occur interstitially between olivine an d pyroxenes. Note augite lamellae in pigeonite are parallel to [100[ plane. McDermott) Introduction to the main analytical methods for geochemical analysis of igneous rocks. Click the microscope button to view a thin section for this sample. In addition to point analysis on individual crystals, an inverted pigeonite crystal and an augite crystal in thin section 14082,6 were also analyzed. Blue and yellow crystals on the top left and lower center are augite, with thin pigeonite exsolution lamellae and twins. Formula: (Mg,Fe,Ca)(Mg,Fe)Si 2 O 6 Monoclinic. White areas show pigeonite and dark areas show augite. 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 … It is crowded with … Photomicrograph of thin section of Moore county, N. c. meteorite. 2.5 mm plag opx h) plag opx cpx 2.5 mm g) 62 Fig. The images were adjusted and combined by … Pigeonite will invert to augite + opx. The pale brownish clinopyroxene displays simple twinning and in some cases distinct chevron-like inverted-pigeonite exsolution textures. DISTINCT OLIVINE & PIGEONITE SUITES, AND OPEN-SYSTEM EVOLUTION. ZAF 4 corrections were applied to the analyses. Inverted Pigeonite. Natural oxides and minerals were used as standards. 5). Frc. This sample is feldspar rich. has Pigeonite. … 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. Inverted pigeonite (15 - 20 modal %) is developed in places. Augite and inverted pigeonite fom Oikocrysts averaging between 3 and 5 cm in (maximum 30 cm). Analytical results … (Photo courtesy Alex Strekeisen; unauthorized reproduction is prohibited.) PPL image, 2x (Field of view = 7mm) Olivine, altered by Iddingsite, clinopyroxene and Plagioclase crystals. 9. The composition of the igneous orthopyroxene did not change because high calcium (2.1 wt% of … The cause for this reduction is unknown. A focused 1-µm beam was used to analyze olivine and plagioclase. Lecture 6: Introduction to Analytical Techniques for Igneous Petrology (Prof. P.F. #20 – Identify the large phenocrysts in this section and give a full description. Pigeonite and augite compositions were resolved with the microprobe in scan mode. The augite, represented by the pinkish-yellow grain to the right, has pigeonite exsolution lamellae. Introduction to cumulus rock terminology and description in advance of practical. PPL image, 2x (Field of view = 7mm) (100) section of Olivine. the thin section and for the oriented pyroxene crystals by electron microprobe (JEOL, JCXA-733) were made by making FIG. The grain initially grew as a twinned monoclinic crystal. inclusions. 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. Thrmlghout the subzone, plagioclase average grain size is variable, ranging to m. Anorthosite I: Textures thin this entire unit are uniform. Methods: A petrographic thin section and a polished chip of A 09545 were used. 1976). 2. was done because the thin section of Y-791538 was lost during thinning and because pigeonite was not present in the RKPA80239 thin section. The pigeonite has inverted to orthopyroxene with augite exsolution. Some grains appear zoned with darker, relatively birefringent cores and paler rims. This forms poikilitic, ... grained clays is pronounced giving the thin section and hand specimen a white speckled appearance when viewed with the naked eye. 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. 2. 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Represented by the x-ray method South Africa with the microprobe in scan mode crust... Not present in the thin section viewed in cross-polarized light at 10x,! 2+ contents, as well as by cation ordering ( Camara et,. These orthopyroxene habits frequently occur together in a few of the clast is some of the thin is.

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