Mining in New Zealand began when the Māori quarried rock such as argillite in times prior to European colonisation. Mining by Europeans began in the latter half of the 19th century. New Zealand has abundant resources of coal, silver, iron ore, limestone and gold. It ranked 22 in the world in terms of iron ore production and 29th in gold production. The total value of mineral production in New Zealand was $1.5 billion in 2006 (excluding oil and gas). The most important metallic minerals produced are gold (10.62 tonnes), silver (27.2 tonnes) and titanomagnetite ironsand (2.15 million tonnes). A 2008 report estimated that the unexploited resources of just seven core minerals (including gold, copper, iron and molybdenum) totalled around $140 billion in worth.