The strategic location of the state on the  hairpin bend of the Himalayas has endowed the land with diverse geological spectrum and rich mineral deposits, mostly covered with large areas of sedimentary deposits attributing to the presence of oil reserves in upper Assam, Digboi, Bongaigaon. Of the four types of coal viz., peat, lignite, bituminous and anthracite, the third kind is readily available in the state. Mikir Hills and North Cachar Hills have substantial reserves of coal. Mikir Hills are also rich in Kaolin (China Clay) deposits. Cachar district of Barak valley has huge storehouse of limestone. Morigaon district contains extensive reserves of granite. Dhubri district of Brahmaputra valley has reserve of more than ten million tonnes of iron ore. Of the four kinds of iron ore, haematite, magnetite, limonite and siderite, the region has reserve of haematite deposits. Nagaon district of central Assam has got very high reserves of glass sand.