A rare green glass spearhead has been found on Western Australia's Rottnest Island during an indigenous studies research trip.
About 50 students from The University of Western Australia were visiting historic sites on the island late last month when the bright emerald green caught a student's eye.
Len Collard from the school of indigenous studies said the spearhead would have been made by a prisoner on the island about 100 years ago, when the island was a prison for indigenous men.
He says spearheads were believed to have been used for trade and exchange, building relationships and hunting quokkas.
"We believe the prisoners would find a place on top of a hill overlooking the mainland where they would make spear tips from scrap pieces of glass," Professor Collard said.
He said a few ceramic and clear glass spearheads had been found before, but it was the first green spearhead, which the students were ecstatic to discover.
Rottnest Island closed as a prison in 1904 and is now a tourist destination.
A UWA spokeswoman said the spearhead was re-buried to respect the Aboriginal tradition of keeping artefacts found in their resting place.