Peanut wood is a form of fossilised wood of dark brown colour with striking peanut-shaped marking. Most specimens are wood from a conifer tree found on the coast of Western Australia. When the trees died, rivers carried them to the salty shallows of the sea at the river mouth. 

They arrived at the sea as a piece of driftwood. This was during the Cretaceous time period when a species of marine clam that loved to eat wood lived in the Australian sea. The clam larvae were able to smell nearby wood and swim to it. When they arrived at a piece of driftwood, they would attach themselves to it and start eating. A tiny pair of valves soon developed on one end of their long body, and they used the sharp edges of their shell as a rasp. They shaved off tiny particles of wood - which they would promptly eat. They could excavate a deep tunnel into the soft, mushy wood in a few weeks.

The sediment then accumulated into these holes and over millions of years formed fossilised peanut wood.

Origin: Western Australia