ASSESSMENT OF THE RUTBA FORMATION SILICA SAND AS ABRASIVE FOR GRINDING AND POLISHING GALENA: A CONTRIBUTION IN ORE MICROSCOPY
This study aims to assess the Iraqi silica sand collected from Rutba Formation as an abrasive for grinding and polishing galena surface for mineralogical study under the reflected light microscope. Grinding is performed using four-grain sizes of silica sand (68, 46, 30, and 18 µm) which are equivalent to 260, 325, 600, and 1200 mesh respectively. Polishing and buffing stages are done using two-grain size of diamond paste (7 and 2.5 µm). The reflectance (R%) values are inversely proportional to the grain size (the lower particle size, the higher the reflectivity), while the surface roughness (Ra) is directly proportional to the grain size. The reflectance is increased from 0, 5.4, 12.2, 16.4, 23.5, 28.3, to 32.3% and roughness is decreased from 57.2, 47.8, 35, 22.5, 8.4, 6.9, to 3.3 µm with grinding and polishing abrasives of grain sizes of 68, 46, 30, 18, 7, and 2.5 µm. The ideal reflectance of the polished surface of galena at 546 nm (air) is 43.1%, and 41.9% at 589 nm in air. The highest reflectance of 32.3% at 546 nm in air achieved by this study is adequate to diagnose galena and its texture intergrowth under the polarized reflected light microscope.