(i) Peninsular rocks contain most of the reserves of coal, metallic minerals mica and many other non-metallic minerals. (ii) Sedimentary rocks on the western and eastern flanks of the peninsula in Gujarat and Assam have most of the petroleum deposits. (iii) The vast alluvial plains of North India are almost devoid of minerals. These variations exist largely due to differences in the geological structure processes and time involved in the formation of minerals.