Gigapixel optical microscopy for meteorite characterization

Ogliore, R. C.; Jilly, C. E.

doi:10.1186/2191-2521-2-3

Cited by 3 publications

(1 citation statement)

References 9 publications

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“…All thin sections were initially studied by optical microscope and mapped using an automated microscopy mapping system developed by Ogliore and Jilly (2013). After carbon-coating, element X-ray maps of each thin section were obtained using the JEOL JXA-8500F electron microprobe at the University of Hawai'i.…”

Section: Cr Chondrite Samples and Petrographymentioning

confidence: 99%

Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses

Jilly-Rehak

Huss

Nagashima

2018

Geochimica et Cosmochimica Acta

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The presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early Solar System; however, the process of aqueous alteration is still poorly understood. Renazzo-like carbonaceous (CR) chondrites are particularly well-suited for the study of aqueous alteration. Samples range from being nearly anhydrous to fully altered, essentially representing snapshots of the alteration process through time. We studied oxygen isotopes in secondary-minerals from six CR chondrites of varying hydration states to determine how aqueous fluid conditions (including composition and temperature) evolved on the parent body. Secondary minerals analyzed included calcite, dolomite, and magnetite. The O-isotope composition of calcites ranged from δO ≈ 9 to 35 ‰, dolomites from δO ≈ 23 to 27 ‰, and magnetites from δO ≈ -18 to 5 ‰. Calcite in less-altered samples showed more evidence of fluid evolution compared to heavily altered samples, likely reflecting lower water/rock ratios. Most magnetite plotted on a single trend, with the exception of grains from the extensively hydrated chondrite MIL 090292. The MIL 090292 magnetite diverges from this trend, possibly indicating an anomalous origin for the meteorite. If magnetite and calcite formed in equilibrium, then the relative O fractionation between them can be used to extract the temperature of co-precipitation. Isotopic fractionation in Al Rais carbonate-magnetite assemblages revealed low precipitation temperatures (~60°C). Assuming that the CR parent body experienced closed-system alteration, a similar exercise for parallel calcite and magnetite O-isotope arrays yields "global" alteration temperatures of ~55 to 88 °C. These secondary mineral arrays indicate that the O-isotopic composition of the altering fluid evolved upon progressive alteration, beginning near the Al Rais water composition of ΔO ~ 1 ‰ and δO ~ 10 ‰, and becoming increasingly O-enriched toward a final fluid composition of ΔO ~ -1.2 ‰ and δO ~ -15 ‰.

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Section: Cr Chondrite Samples and Petrographymentioning

confidence: 99%

Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses

Jilly-Rehak

Huss

Nagashima

2018

Geochimica et Cosmochimica Acta

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Exomorphogenesis of Cosmogenic Ring Structures of Kazakhstan

Veselova

Kasymkhanova

Kozhakhmetova

et al. 2019

Journal of Landscape Ecology

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The use of materials for remote sensing of the Earth made it possible to identify a new type of crustal structures and features of their expression in relief. These are ring structures that complicate the structure of the studied structures of a linear type. As a result of the study of the morphology, geological and tectonic structure of ring structures, it was established that they represent formations of various origins: pluton-volcanic, cosmogenic, and anthropogenic. Cosmogenic structures of different ages and differ in various degrees of transformation. The relief of the identified cosmogenic structures within the limits of the Turan Plains, the Kazakh small hills and mountains of South-Eastern Kazakhstan is transformed by exogenous processes. The defining indicator features of cosmogenic structures include geomorphological, geological, structural tectonic, and also landscape. The degree of change in the initial cosmogenic relief depends on the time of formation, paleogeographic and modern physiographic conditions of the territories. Under the arid conditions of Kazakhstan’s epyhercynian platform, the main factor in the preservation of the “primary” morphology of meteorite craters is the lithologic stratigraphic complexes of the ring shaft. For the studied cosmogenic structures, in particular, the meteorite craters of Saryarka, a distinct geodynamic zoning of the development of exomorphogenesis processes is characteristic. The main exogenous processes include gravity-slope, surface washout, ravine and river erosion, processes of complex denudation and accumulation. The factors and processes of creating a modern crater relief morphology are established. These studies of cosmogenic ring structures of Kazakhstan have not only theoretical significance, revealing the role of cosmogenic processes of the formation of the Earth as a planet, but also have immediate practical importance. Meteorite craters are indicators of mineral deposits.

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Petrographic Microscopy with Ray Tracing and Segmentation from Multi-Angle Polarisation Whole-Slide Images

Zamora

Kamber

2023

Minerals

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‘Slide scanners’ are rapid optical microscopes equipped with automated and accurate x-y travel stages with virtual z-motion that cannot be rotated. In biomedical microscopic imaging, they are widely deployed to generate whole-slide images (WSI) of tissue samples in various modes of illumination. The availability of WSI has motivated the development of instrument-agnostic advanced image analysis software, helping drug development, pathology, and many other areas of research. Slide scanners are now being modified to enable polarised petrographic microscopy by simulating stage rotation with the acquisition of multiple rotation angles of the polariser–analyser pair for observing randomly oriented anisotropic materials. Here we report on the calibration strategy of one repurposed slide scanner and describe a pilot image analysis pipeline designed to introduce the wider audience to the complexity of performing computer-assisted feature recognition on mineral groups. The repurposed biological scanner produces transmitted light plane- and cross-polarised (TL-PPL and XPL) and unpolarised reflected light (RL) WSI from polished thin sections or slim epoxy mounts at various magnifications, yielding pixel dimensions from ca. 2.7 × 2.7 to 0.14 × 0.14 µm. A data tree of 14 WSI is regularly obtained, containing two RL and six of each PPL and XPL WSI (at 18° rotation increments). This pyramidal image stack is stitched and built into a local server database simultaneously with acquisition. The pyramids (multi-resolution ‘cubes’) can be viewed with freeware locally deployed for teaching petrography and collaborative research. The main progress reported here concerns image analysis with a pilot open-source software pipeline enabling semantic segmentation on petrographic imagery. For this purpose, all WSI are post-processed and aligned to a ‘fixed’ reflective surface (RL), and the PPL and XPL stacks are then summarised in one image, each with ray tracing that describes visible light reflection, absorption, and O- and E-wave interference phenomena. The maximum red-green-blue values were found to best overcome the limitation of refractive index anisotropy for segmentation based on pixel-neighbouring feature maps. This strongly reduces the variation in dichroism in PPL and interference colour in XPL. The synthetic ray trace WSI is then combined with one RL to estimate modal mineralogy with multi-scale algorithms originally designed for object-based cell segmentation in pathological tissues. This requires generating a small number of polygonal expert annotations that inform a training dataset, enabling on-the-fly machine learning classification into mineral classes. The accuracy of the approach was tested by comparison with modal mineralogy obtained by energy-dispersive spectroscopy scanning electron microscopy (SEM-EDX) for a suite of rocks of simple mineralogy (granulites and peridotite). The strengths and limitations of the pixel-based classification approach are described, and phenomena from sample preparation imperfections to semantic segmentation artefacts around fine-grained minerals and/or of indiscriminate optical properties are discussed. Finally, we provide an outlook on image analysis strategies that will improve the status quo by using the first-pass mineralogy identification from optical WSI to generate a location grid to obtain targeted chemical data (e.g., by SEM-EDX) and by considering the rock texture.

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Gigapixel optical microscopy for meteorite characterization

Cited by 3 publications

References 9 publications

Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses

Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses

Exomorphogenesis of Cosmogenic Ring Structures of Kazakhstan

Petrographic Microscopy with Ray Tracing and Segmentation from Multi-Angle Polarisation Whole-Slide Images

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