Photomicrographs of Portland Cement Raw Materials

Photograph 10-1 Kiln feed in thin section. Multicolored particles are grains of dolomitic limestone (calcite). Gray quartz at lower right, feldspar at upper right. Clinker produced contains an abundance of belite nests and periclase. (S A6869) 

Photograph 10-2 Feed particles representing the insoluble residue from acetic acid in a thin section which is slightly thicker than normal. Gray and yellow quartz, microcline feldspar (arrow), and other silicates. 

Photograph 10-3 Thin section of kiln feed containing an abundance of coarse micaceous siltstone (arrows), providing the silica for the clinker and producing a uniform distribution of clinker silicates, suggesting the ease with which combination can occur with finegrained, polycrystalline, impure, siliceous raw materials. (S A6871) 

Photograph 10-4 Thin section of 125-pm fraction of raw feed showing twinned feldspar (left) surrounded by fine- to medium-crystalline limestone, with ferro-magnesian silicate (hornblende) on right. (S A6872) 

Transmitted, plane-polarized light Field dimensions = 0.6 mm x 0.6 mm 

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FIG. 10—This plane polarized photomicrograph illustrates a residual grain of Rosendale natural cement circa 1850. Rhombic-shaped crystals of calcined dolomite are surrounded by reddish rims of an ironbearing mineral phase (arrow). Note the similarity to the laboratory produced cement depicted in Fig. 9. This microtexture is diagnostic of natural cements produced from dolomitic raw materials and is never observed in portland cements or limes. (See color insert for color version of this figure). 

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