Petrographic Identification of Raw Feed Constituents

Microscopical examination should start in the quarry where samples of each of the varieties of limestone, sandstone, shale, etc., are collected, layer by layer, by a geologist or someone with an adequate knowledge of the quarry. An assumption of the mineralogy of most quarried materials, as well as many of the industrial byproducts, is commonly questionable. Representative portions of each rock variety are sent off, if necessary, for thin sectioning (see partial list of professional companies in Table 11-3). Some of these companies will also stain the thin sections as directed. Another portion of the rock is crushed in the plant laboratory with a mortar and pestle or other suitable crushing device, and sieved to produce a 45- to 75- im fraction for examination in a powder mount, using, at first, a liquid with a refractive index of approximately 1.542. Samples of nondeposit materials, such as slag, fly ash, bottom ash, rice husk ash, clay catalyst, etc., are examined similarly. 

Insoluble residues from a portion of this sieve fraction can be prepared with 20% acetic acid and 20% HCl the residue is then sieved to retain the 45- im material which can then be studied in powder mount, thin section, or both. The difference in the two residues is related to dolomite percentage. 

Commercially prepared thin sections (Table 11 -3) are studied along with the powder mounts in order to see which features of the whole rock can be observed in the powder particles, thus facilitating their 

Certain minerals in cement raw materials examined in thin sections or sieved powders can be selectively stained with a wide variety of liquids (Carver, 1971 Hutchison, 1974) and studied with a stereomicroscope and a petrographic microscope. The stains are normally used to augment data from ordinary optical microscopy. 

Mineral characteristics in transmitted and reflected light are clearly described in standard optical mineralogy texts (Heinrich, 1965 Kerr, 1977). The optical properties of almost all known minerals, with a concise description of optical theory and technique, are given by Fleischer, Wilcox, and Matzko (1984) who emphasize particle-mount analysis. 

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