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Igneous Petrology and the Nature of Magmas
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
High magnification can reveal things not seen otherwise, so petrologists often study rocks using a microscope. The microscope shown in Figure 5.7 is a polarizing petrographic microscope, a fundamental tool of petrologists. It is similar in most ways to other types of microscopes, except that the light that comes from below the stage passes through a polarizing filter, and a second polarizing filter can be inserted in the column above the stage. The filters allow some rock and mineral properties to be observed that otherwise could not be seen. Petrographic microscopes reveal details that permit more accurate mineral identification and, often, reveal information about rock crystallization history. Petrography is the general term for the descriptive part of petrology that involves outcrops in the field, hand samples, and thin sections. Petrologists use the descriptive information to interpret rock petrogenesis—the origin and nature of the processes that created a rock.
Stone testing
Published in Dolores Pereira, Natural Stone and World Heritage, 2019
Each stone is suitable for a specific purpose. Suitability is determined by the careful study of the physical and mechanical characteristics, all of which are directly related to the mineralogy and texture of the stone. Mineral composition consists of essential (main constituents) and accessory (minor constituents) minerals but also secondary minerals, derived from the weathering of the first two. Analysis requires a detailed description (petrographic study) relating to both the macroscopic properties of the rock by visual evaluation of hand specimens, and the microscopic properties by a thin section evaluation using a petrographic microscope (ASTM, 2015a). The resulting petrographic description characterises the colour, fabric, mineralogy, grain size, cracks, cavities and evidence of weathering and alteration in both hand specimens and thin sections.
Tests to determine the abrasiveness of rock
Published in Peter N.W. Verhoef, Wear of Rock Cutting Tools, 2017
To determine the wear factor, thin sections of the rock materials under consideration have to be prepared for microscopic examination. Using the petrographic microscope, the mineral content and the grain size of the minerals can be determined. Thin sections can be made of the same rock disc on which the Brazilian tensile strength test is carried out. For example, a sandstone may have the following composition:
High-temperature–low-pressure metamorphism and the production of S-type granites of the Hillgrove Supersuite, southern New England Orogen, NSW, Australia
Published in Australian Journal of Earth Sciences, 2018
Samples were collected and field observations made for the Tobermory (W0807) and Rockvale (W0809) monzogranites, and the Abroi Granodiorite (W0514, W0603) / Gneiss (W0542). Polished thin-sections were prepared for microscopic examination, using a petrographic microscope in combination with the Virtual Petrographic Microscope (Tetley & Daczko, 2014), and Electron MicroProbe (EMP) analysis. Thin-section photomicrographs were taken on a Nikon 50iPOL petrographic microscope with Nikon DS-Fi1 digital camera and Nikon NIS Elements-D software for multiple photograph stitching. Representative rock samples were selected for whole-rock analysis and the preparation of zircon concentrates by Geotrack International (Melbourne). Zircon mounts were prepared for imaging, U–Pb geochronology and Hf isotope analysis.
Long distance kelp-rafting of rocks around southern New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2018
Some rock specimens were sufficiently large and robust for adequate rock identification in hand specimens, and with stereomicroscopy, of coarse-grained rocks. Finer-grained robust specimens permitted standard polished thin section preparation procedures, followed by examination with a petrographic microscope. However, many rock remnants formed only thin veneers (millimetre scale) on the holdfasts and remained fragile even after drying. These veneers were examined by light stereomicroscopy to identify key mineralogy and textures. A selection of more robust rock specimens, with minimal residual organic components, has been archived in Geology Department, University of Otago (Table 1).
Self-heating characteristics of materials for producing activated carbon
Published in International Journal of Coal Preparation and Utilization, 2020
Jibril Abdulsalam, Moshood Onifade, Jean Mulopo, Samson Bada
Three materials for producing activated carbon collected from the Witbank Coalfields were used. The samples were stored in an airtight bag to prevent further oxidation. They were pulverized to −250 µm size for the proximate and ultimate analysis and −212 µm for the spontaneous combustion tests. The proximate analyzes for the samples were performed according to the American Society for Testing and Materials (ASTM, D5142). One (1 g) each of the sample was used to calculate the moisture, ash and volatile matter contents, while the fixed carbon was calculated as the subtraction of volatile matter, ash and moisture contents from 100%. For the ultimate analysis, 0.25 g of each coal was used at a temperature up to 1,450 °C with an analyzing time between 60 and 300 seconds according to the ASTM (ASTM, D5373-14:2015) for carbon (C), hydrogen (H) and nitrogen (N) with the use of a LECO CHN 628 with an add on 628 S module. Maceral analyses, including mineral matter, was performed using a Zeiss Axio Imager M2m (model) reflected light petrographic microscope to examine the various organic and inorganic content of the samples. The petrographic blocks were prepared to a fine polish using 0.05 µm OPS solution to achieve a scratch-free surface, according to the South African National Standard (SANS, 7404 Parts 1–5). The macerals results are reported as volume percent (vol.%), inclusive of mineral matter (in.mmf) basis. The classification of macerals is based on the classification of the International Committee for Coal and Organic Petrology (ICCP, 1998, 2001). Vitrinite reflectance was carried out on the samples indicating the coal samples are Medium Rank C Bituminous. The experimental results for the samples are discussed below.