The Prospect dolerite intrusion, or Prospect intrusion, is a Jurassic picrite or dolerite laccolith that is situated in Sydney, New South Wales, Australia. Lying in the heart of Cumberland Plain, in the suburb of Pemulwuy (previously Greystanes), the intrusion is Sydney's largest body of igneous rock, rising to a height of 117 metres (384 ft) above sea level. The site is formed by an intrusion of dolerite rock into Ashfield Shale. At least seven different rock types occur in the intrusion.