Proven mineral resources in Jiangsu include manganese, copper , iron, phosphorus, coal, petroleum, limestone, pottery clay, serpentine, gypsum and marble. Rice and wheat are the main food crops, while cotton, rapeseed and peanuts are important cash crops. Its cotton accounts for a quarter of China's total output. With a coastline of over 1,000 kilometres and wide expanses of fresh water, the province is highly suitable for the development of fisheries and aquaculture.