Carbon occurs in nature in free state as well as in combined state.
1) Free state: Diamond , Graphite , Coal
2) Combined state :
Gaseous state: 1) In the atmosphere, 2) As a natural gas and petroleum gas
Liquid state: 1) Natural waters - Soluble carbonates and bicarbonates
Solid state: 1) In wood (cellulose)
2) Mineral deposits of metallic carbonates