Rock-Soil Transition In Weathering Of A Porphyritic Biotite Granite

Concentric layers of weathered materials around core-stones show the porphyritic biotite granite to experience sequential, but gradational, changes in visible features, textures and mineralogy as it transforms from ‘rock’ into ‘soil’. The start with opening-up grain boundaries micro-cracks (stage 1) followed by their dark brown staining 2) subsequent alteration (to sericite clay minerals) groundmass plagioclase feldspar grains 3). Biotite flakes are then bleached altered chlorite 4) before there starts alkali 5) finally phenocrysts 6). Quartz not during these stages weathering, disaggregate reduce size due continual micro-cracks. Increasing weathering marked decreasing dry unit weights, densities uniaxial compressive strengths, increasing apparent porosities. transition between ‘soil’ occurs stage 6 when all plagioclase, most feldspar, have been some phenocrysts. Stage is large porosities (>18%) low values weight (<20.81 kN/m3), density (<2,122 kg/m3) strength (<1.8 MPa).