Granitic rocks

Around Melbourne's fringes are a number of outcrops of coarse grained igneous intrusive rocks commonly referred to as granite. The granitic rocks around Melbourne are mainly granite or granodiorite. The granites in the Melbourne region are Upper Devonian in age and have intruded the Silurian to Lower Devonian siltstone and sandstones which form the bedrock of the region. The Tertiary and Quaternary were also periods of significant volcanic activity in the vicinity of Melbourne. Detailed joint orientation information is available from several sites in the Melbourne Region. The strength of granite increases as weathering decreases where it has been observed in the Melbourne region. Soil strength data for extremely weathered granodiorite is extremely limited and should not be considered as necessarily representative of extremely weathered granites in general. Granite is composed of a large percentage of feldspar minerals which are altered to clay minerals by weathering processes.