Mineral grains, individual

The raw ROM (run of mine) ore is reduced in size from boulders of up to 100 cm in diameter to about 0.5 cm using jaw cmshers as weU as cone, gyratory, or roU-type equipment. The cmshed product is further pulverized using rod mills and ball mills, bringing particle sizes to finer than about 65 mesh (230 p.m). These size reduction (qv) procedures are collectively known as comminution processes. Their primary objective is to generate mineral grains that are discrete and Hberated from one another (11). Liberation is essential for the exploitation of individual mineral properties in the separation process. At the same time, particles at such fine sizes can be more readily buoyed to the top of the flotation ceU by air bubbles that adhere to them. 

Laser Microprobe Argon-39—Argon-40 Dating of Individual Mineral Grains... 

Electron microprobes can be used in spot mode to measure the chemical compositions of individual minerals. Mineral grains with diameters down to a few microns are routinely measured. The chemical composition of the sample is determined by comparing the measured X-ray intensities with those from standards of known composition. Sample counts must be corrected for matrix effects (absorption and fluorescence). The spatial resolution of the electron microprobe is governed by the interaction volume between the electron beam and the sample (Fig. A.l). An electron probe can also be operated in scanning mode to make X-ray maps of a sample. You will often see false-color images of a sample where three elements are plotted in different colors. Such maps allow rapid identification of specific minerals. EMP analysis has become the standard tool for characterizing the minerals in meteorites and lunar samples. 

Individual and non-destructive chemical analysis of microscopic remnants enclosed in mineral grains has been proven possible by certain spectroscopic techniques such as Raman-, IR-, UV/visible- and Laser mass spectroscopy (Pflug, 1982)16>. 

Solutions of the diffusion equation inevitably involve the dimensionless parameter Dtla2 in such a way that diffusive redistribution becomes significant as this parameter approaches unity. Here a is some characteristic dimension of the diffusive region. In the case where the medium is homogeneous, without a microscopic substructure (e.g., a glass or a liquid), a is the macroscopic dimension. In rocks that consist of numerous mineral grains, the relevant a is usually the individual grain size rather than the macroscopic dimension. 

In the past decade, there has been a growing awareness that the study of mineral behavior has important implications in related disciplines in the earth sciences, even to the level where continental-scale tectonic phenomena are being considered in terms of processes taking place within individual mineral grains. Although some important properties of crystalline materials can be understood in terms of ideal crystal structures (as determined by x-ray diffraction), many of the physical and chemical... 

Brittle deformation involves fracturing on the scale of individual mineral grains or larger,... 

The more fundamental approach to addressing the physical dimensions involved in weathering is to characterize the surface areas of the individual minerals, i.e., the specific mineral surface area S (m g )- The extent to which this specific surface area scales directly with the reactive surface areas in natural environments is a matter of considerable debate, particularly in regard to the accessibility of water. For unsaturated environments, such as those in most soils, the wetted surface area may be considerably less than the physical surface area of contained mineral grains (Drever and Clow, 1995). In addition, surface areas of microscopic features such as external pits and internal pores may be associated with stagnant water that is thermodynamically saturated and not actively involved in weathering reactions (Oelkers, 2001). 

Isotopic and Geochronologic Measurements on Individual Mineral Grains Contrasting Provenance of H3 and H6... 

Without detailed descriptions of individual particle geometry, mineral grains are normally characterized by length or diameter, 3, which represents a range of lengths. The specific surface area is then defined as... 

A number of techniques have been used to determine mineralogies of coal As discussed in a recent review (J ) the most common techniques are x-ray diffraction infrared spectroscopy optical microscopyy and electron microscopy. X-ray diffraction and infrared spectroscopy can be considered "bulk methods because they are generally best performed on the mineral-matter concentrate obtained by removal of the macerals by low-ten5>era-ture ashing ( 2 ) The microscope methods can be considered "particulate methods because mineral grains in the coal are sized and classified individually These microscope methods are usually used without separation of minerals and macerals because the coal macerals can serve as a background matrix to separate mineral particles and to provide contrast for the dimensional measurement of the particle ... 

Improvements in the technology of analytical instruments that have occurred since the measurements in Table 19.5 were made permit individual mineral grains to be dated by the Rb- Sr, Ar/ Ar, and U-Pb methods. The crystallization ages of selected mineral grains in till... 

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