PETROGRAPHY OF CRYSTALLINE ROCKS: STIMULUS OF ABRASION RESISTANCE

As a precursor to the determination of how petrography stimulates abrasion resistance of crystalline rocks, six different types were tested for their petrographic characteristics and abrasion resistance. Further petrographic analysis was carried out with ImageJ. The petrography showed that the rock types contain quartz (ranging from 16 to 29%), plagioclase (21 to 36%), biotite (5 to 41%), microcline (0 to 41%) as major minerals. The accessories include zircon, mymerkite and opaque minerals. Texturally, lamprophyre exhibited porphyritic texture by displaying relatively large biotite crystals in very fine groundmass of biotite, hornblende, quartz and feldspar. Porphyritic biotite granite also exhibited porphyritic texture. Other rock types exhibited medium to coarse textural characteristics. All the rock types exhibited micro-structures to varying degrees with charnockitic rocks displaying more varieties and quantities while gneiss and granite gneiss tend to possess fewer varieties and quantities. Lamprophyre possessed the highest abrasion resistance (Ha) of 34.40 while granite gneiss possessed the least value of 26.50. Quartz plus feldspar (Q+F) content (%) presented the highest correlation coefficient of -0.7206 with abrasion resistance. When the outlier was removed, the correlation coefficient increased to -0.9620. The mathematical model, Ha = -0.4006(Q+F) + 53.692, was derived for the relationship between (Q+F) content (%) and abrasion resistance. A standard deviation of 0.94 was evaluated from relating the abrasion resistance values determined in the laboratory with the values estimated with the derived mathematical model. The model is not reliable as all estimated values were not accommodated within the range 29.18 and 36.70 (mean ± 4*standard deviation). It was, however, discovered that grain interlock and texture have more influence on the abrasion resistance of rocks than mineral content and micro-structural characteristics.