Located on a gently undulating plain of quartz gravel, 100 kilometres south of the Northern Territory town of Tennant Creek, the Devils Marbles are giant granite domes, some standing isolated, others balancing precariously one top of another. They are the only distinctive natural landmark for hundreds of square kilometres. The marbles vary from less than a metre to as much as 6 metres in diameter. They are derived from a single mass of granite which crystallised more then 150 million years ago
