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TECHNICAL PAPER

Figure 6: (a) Calcite with pyroxene mineral augite [21] ; (b) Calcite with apatite, chlorite and hornblende [21] ; (c & d) River sand grains under polarized
microscope; (e) River sand in thin section; (f) Weathered quartz grain in river sand [21] , (g, h, i, j, k & l) Recrystallizing phases of quartz and altering phases
of feldspars in thin sections
colour interferences in the same plane [21] . Figure 6 (g, h and i) Another prominent variant of limestone rock, with a very
indicates various sites in river sand, in which aggregates different microstructure is coral limestone. They are sedimentary
fragments with a granitic source are getting weathered. In rocks, but of organic in nature as the formation arises out of
Figure 6 (g, h, i), the pockets of quartz grains with micro coral reefs from marine ecosystem by polyps generally, which
crystalline features are getting eroded along with feldspar. are essentially multicellular organisms. Aragonite deposition is
Feldspars disintegration, and conversion into clay minerals are prominent in the calcareous exoskeleton which are sourced from
visible in Figure 6 (h). These alterations are more prominent, and the carbonate and calcium ions in the marine environment along
illustrated in thin section images provided in Figure 6 (j, k and l). with other minerals such as calcite and quartz. The peculiarity

16 THE INDIAN CONCRETE JOURNAL | AUGUST 2022