Seeds from the Tung tree, used for wood workers oil. These trees were planted in a plantation, but the seeds never harvested.
The fruit is about the size of a small lime. I had never seen one before this.
(Tung oil or China wood oil is a drying oil obtained by pressing the seed from the nut of the tung tree (Vernicia fordii). The oil and its use are believed to have originated in ancient China and appear in the writings of Confucius from about 400 B.C.)