Polished sections

Sketch the structures that you would expect to see if you looked at polished sections of the samples under a reflecting light microscope. Label the phases, and any other features of interest. You may assume that each specimen has been cooled moderately slowly from a temperature of 1100°C. 

Figure 6.17 Phase contrast micrograph of a polished section of a dental silicate cement, showing angular glass particles, size 1 to 100 pm, embedded in a featureless matrix (Wilson et at., 1972).

As shown in Fig. 1.117, Se-type and Te-type epithermal Au-Ag vein-type deposits are located in the Cretaceous-Quaternary volcanic terrane of Japan (e.g., northeast and southwest Hokkaido, middle Honshu, south Kyushu). Some Te-type deposits are located in regions similar to the Se-type deposits. Sometimes, Te mineralization is associated with the Se-type deposits, though Te minerals usually do not coexist with Se minerals. However, rarely, Te minerals coexist with Se minerals in the Te-type deposits (e.g., Teine, Suzaki, Kawazu, Iriki) on a polished section scale. For example, coexistence of native Te and Se-bearing tetrahedrite is found at Teine. Generally, Te mineralization occurs at... 

Ilmenite-series and magnetite-series granitic rocks are defined as follows (Ishihara, 1977) the magnetite-series and ilmenite-series granitic rocks are distinguished by the presence or absence, respectively, of magnetite in polished sections. 

Microscopic observation suggests that stannite formed earlier than stannoidite on the scale of one polished section, although in general coexistence of stannoidite and stannite cannot be observed in the same polished section. If stannite formed at an earlier stage than stannoidite, it could be inferred that /sj increased or that temperature decreased (or both) with evolution of tin mineralization. 

The eutectics examined and their melting points are given in Table 3.1. The compounds were melted in 10 mm inner diameter pyrex tubes, and polished sections were prepared from the solidified eutectic samples. 

Fig. 2. EPMA back-scattered electron images of a polished section from Chelehkureh deposit, a) carbonate in a mineralized vein with chalcopyrite b) larger image of carbonate grain marked by + in previous image, c), d) and e) are in turn compositional Mg, Fe and Ca images of that grain.

This investigation relied on petrographic analysis of polished sections using reflected light and the scanning electron microscopy (SEM) and electron microprobe (EPMA) analyses to identify minerals and to document the distribution of gold. The mineralized zone is coincident with a distinct bleached alteration zone that contains fine- to coarse-grained, subhedral arsenopyrite and pyrite in quartz-carbonate veins. 

Work concentrated on gangue quartz in main gold-bearing sulfides veins, and in late stage intrusion-related ( ) base-metal veins. Polished sections were first investigated by transmitted and reflected light microscopy to find suitable samples... 

To enable detection of fine mineral particles (<20pm),back-scattered electron imaging was used. Once the minerals were detected, EDS was used for analysis. Selected lignite particles were scanned to determine the distribution of minerals. Mineral types were then differentiated by variation in back scatter intensity and identified using EDS. The relative proportions (major, minor) and size and spatial distributions of the minerals were recorded. The overall surface of the polished section was viewed and massive minerals were analyzed and their distribution and size recorded. 

Reflected light microscopy can be used either on thin sections or thicker polished sections. Reflected light is used primarily for identifying opaque minerals such as metals, sulfides, and some oxides. Each of these minerals has a unique appearance in reflected light. 

Raman spectroscopy is a non-destructive technique that is used in cosmochemistry for identification of minerals and to evaluate the bonding and composition of organic molecules. The technique does not require special sample preparation raw rock samples, polished sections, fine-grained powders, and liquids can be analyzed. Raman spectroscopy is the basis for several instruments that are under consideration for upcoming NASA missions. 

Mackowsky discusses the mineral phases found in coals and differentiates those phases with geologically different genetic histories. A number of the mineral phases are shown in a series of photomicrographs of polished sections of coals. 

Polished sections and polished thin sections are prepared according to the usual techniques of coal petrography. They are mounted permanently on quadrangular pieces of transparent Lucite for location purposes. We have described elsewhere a graphical method of micro-surveying which allows an observer to locate any specific autoradiograph on nuclear emulsion plate of a given point in an opaque section (13). 

Coal from Dorenaz, Valais, Switzerland. This anthracitic coal of Carboniferous age shows interesting peculiarities (Figure 5). In contrast to the former case, the a-activity is arranged along lines parallel to the bedding, either as stars or as bands (Figure 5d, e). In the polished sections one observes elliptical halos without specific mineral inclusions or bands of very fine black particles. The anisotropy effects are very marked as different kinds of crosses or vivid bands (Figure 5a, b). 

Figure A. Megaspore from a high volatile bituminous coal (37% V.M.), on the left changed by a-irradiation polished section, oil immersion, X 100 (from Brennstoff-Chemie 46, 13 (1965))...

Figure 10. The effect of compression on a xylite (wood) from a soft brown coal (with 60% moisture) (left) as mined (right) compressed at a pressure of ca. 270 kg./sq. cm. Polished sections under oil immersion, X 250...

Peter A. Hacquebard The differentiation of various vitrinic compounds so beautifully shown in the Brandon lignite—e.g., between cell wall material and cell-content material, can also be observed in bituminous coals. I have been able to show this on polished sections by using an etching technique. How has Dr. Spackman shown this in thin sections, and what would be the effect of rank increase on the existence of these two types of vitrinite—i.e., types derived from cell walls and cell contents ... 

Nakhla F. M., 1956, The hardness of minerals in polished sections, Econ. Geol., 51, 811-817. 

The Mackensen blower method is found to be harder to relate to Vickers hardness determined by diamond indenter, although analysing the results of tests carried out by the two methods on ceramic grinding wheels using alundum as the abrasive (A. Szymanski, 1968c), results qualitatively similar are observable (Fig. 4.5.12). Alundum grains, size 8 (3.15-2.50 mm), were moulded in a ceramic binder and fired at various temperatures ranging from 1470 to 1630 K, with one-hour time delay. Polished sections were... 

A. Szymariski (1972) tested the hardness of porcelain bodies sintered at various temperatures, in the 1475-1713 K range, and demonstrated the existence of a correlation between the mean Mackensen-Mohs hardness and the degree of porosity of a body, determined on polished sections with an Opton analysing microscope, and also the sintering contraction due to sintering determined using the Leitz-Wetzlar heating-microscope (Fig. 8.3). The above tests were carried out on porcelain body samples collected... 

Mixtures of powders of poly(vinyl chloride) (FVC) and various metals were compacted at a pressure of 10,000 psig at 120-130°C. The compacts appear to be strong, and density measurements show the porosity to be <1.5%, Electrical resistivity is reduced, from a value for unloaded FVC of about JO25 Clem, to < JO"1 Clem by a fractional volume loading of nickel or copper as low as 0.06. Microscopic examination of polished sections of the compacts show the metallic particles to be segregated around zones of unpenetrated polymer which correspond in size to the initial particles of FVC. The pattern of segregation favors the formation of continuous chains of metallic particles at unusually low volume loadings. 

Low-magnification SEM micrograph of polished sections, showing three-dimensional representations of the submillimeter structure of two architectures of Si3N4/BN FM (adapted from ref. [29]). 

The polished samples are sputtered with a thin layer of gold for analysis in a scanning electron microscope (SEM), a Jeol JSM 35c fitted with a link AN 10000 energy-dispersive X-ray spectrometer (EDS). The fractured surfaces and polished sections through fractured specimens can also be prepared and analysed in this manner. SEM analysis may reveal a non-uniform fibre distribution in the composite. In composites sintered at different temperatures, cracking in the matrix phase and residual porosity can be identified and the filler particles are discernible. The EDS indicates the higher particles and the matrix constituents. 

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