Sixteen ethnic groups inhabit Sierra Leone, the two largest and most influential being the Temne and Mende peoples. About 2% of the country's population are Krio, descendants of freed African American and West Indian slaves. English is the official language used in schools and government administration; however, Krio is the most widely spoken language across Sierra Leone, spoken by 97% of the country's population. Sierra Leone is very rich in natural resources, especially diamond, gold, bauxite and aluminum. The country is a member of the United Nations, African Union, Economic Community of West African States (ECOWAS), Mano River Union, Commonwealth of Nations, African Development Bank, and Organisation of Islamic Cooperation.