The Inter-relationship of Bulk Density and Porosity of Some Crystalline Basement Complex Rocks: A Case Study of Some Rock Types In Southwestern Nigeria

Abstract

The inter-relationship of bulk density and porosity of some crystalline rocks in southwestern Nigeria was investigated. Six crystalline basement complex rock types from two localities in Nigeria (three each from Akure and Igarra) were sampled and tested for their petrography (mineralogy, texture and microstructures), bulk density and porosity. ImageJ was used for image analysis of the photo-micrographs, the bulk density was calculated from the determined specific gravity while the porosity was determined by water saturation technique. From the results of the analyses, the rocks were found to contain quartz, feldspar, hornblende, mica and minor minerals in various proportions. Micro-structures such as bent twin lamellae, undulose extinctions, distorted and incomplete twining and platy mineral alignment were observed in the thin sections of the rocks. The bulk density values ranged from 2.63 to 2.81 and the porosity from 0.03 to 0.16. The correlation coefficient relating the two parameters is -0.9713 indicating a very high negative correlation. The square of Pearson Product moment correlation coefficient is 0.9434. A mathematical model was derived from the relationship between the two parameters. The standard error of 0.02 and the Ftest of 0.98 were determined for the model. It was deduced that the porosity of a crystalline rock is affected mainly by its bulk density and possibly by the degree of weathering.