He thought he’d struck gold in Victoria’s historic fields. Instead, a stubborn, unbreakable rock that defied saws, acid, and a sledgehammer hid a secret billions of years in the making. David Hole spends his weekends doing what plenty of men his age do around Maryborough, a small town northwest of Melbourne. He drives out to the regional park, unpacks his metal detector, and walks the yellow clay soils listening for the signal that ... [5049 chars]