Kaolinite

Originally a secret well-kept from prying western eyes for many hundreds of years, China's deposits of a 'wonder clay' remained unknown. The production of pottery and fine porcelain made from the clay remained one of China's most remunerative exports. Eventually (in the early 1700s) the French Jesuit missionary Pere d'Entrecolles exposed the secret by bringing samples of the clay back to Europe. There it was discovered that the essential ingredient of the clay was the mineral kaolinite. From that point kaolinite deposits were identified world-wide including the large deposits in Cornwall.