Truong Van Dai never thought a stone he came across seven years a go could be of any value.
Dai found the stone while he was working at Hoang Mai quarry in central Vietnam and thought its shape and color strangely resembled that of a snail.
He brought it home and, after a while, used it to chock mobile scaffolding - until recently when some of his friends suggested that he could contact scientists at the Vietnam National Museum of Nature about the weird looking object.
The scientists at the Hanoi-based museum found out that the stone indeed a mollusc fossil, measuring 145 mm (5.7 in) in height, 130 mm (5.1 in) in width, and 7 mm in thickness.
Dr Nguyen Huu Hung, an expert at the museum, said the fossil may date back to between 242 million years and 247 million years.
The scientists at the museum have confirmed that the mollusc fossil was a species of Naticopsis, an extinct genus of gastropod.
Hung said the fossil is the biggest of all the specimens from the Triassic period ever discovered in the Vietnam.