producer of vanadium; the 6th largest world producer of iron ore; the 11th largest world producer of cobalt; and the 15th largest world producer of phosphate. It was the world's 12th largest producer of uranium in 2018. Mining has been the main driving force behind the history and development of Africa's most advanced economy. Large-scale and profitable mining started with the discovery of a diamond on the banks of the Orange River in 1867 by Erasmus Jacobs and the subsequent discovery and exploitation of the Kimberley pipes a few years later. Gold rushes to Pilgrim's Rest and Barberton were precursors to the biggest discovery of all, the Main Reef/Main Reef Leader on Gerhardus Oosthuizen's farm Langlaagte, Portion C, in 1886, the Witwatersrand Gold Rush and the subsequent rapid development of the goldfield there, the biggest of them all. South Africa is one of the world's leading mining and mineral-processing countries. Though mining's contribution to the national GDP has fallen from 21% in 1970 to 6% in 2011, it still represents almost 60% of exports. The mining sector accounts for up to 9% of value added. In 2008, South Africa's estimated share of world platinum production amounted to 77%; kyanite and other materials, 55%; chromium, 45%; palladium, 39%; vermiculite, 39%; vanadium, 38%; zirconium, 30%; manganese, 21%; rutile, 20%; ilmenite, 19%; gold, 11%; fluorspar, 6%; aluminium, 2%; antimony, 2%; iron ore, 2%; nickel, 2%; and phosphate rock, 1%. South Africa also accounted for nearly 5% of the world's polished diamond production by value. The country's estimated share of world reserves of platinum group metals amounted to 89%; hafnium, 46%; zirconium, 27%; vanadium, 23%; manganese, 19%; rutile, 18%; fluorspar, 18%; gold, 13%; phosphate rock, 10%; ilmenite, 9%; and nickel, 5%. It is also the world's third largest coal exporter. The mining sector has a mix of privately owned and state-controlled mines, the latter including African Exploration Mining and Finance Corporation. Agriculture and food processing In 2018, South Africa produced 19.3 million tonnes of sugarcane (14th largest producer in the world), 12.5 million tonnes of maize (12th largest producer in the world) 1.9 million tons of grape (11th largest producer in the world), 1.7 million tons of orange (11th largest producer in the world) and 397 thousand tons of pear (7th largest producer in the world). In addition, in the same year, it produced 2.4 million tons of potato, 1.8 million tons of wheat,