Stories about the skulls focus heavily on their perceived supernatural powers.
Greenstone and Jade are all the same thing. Pounamu was the name the Maori people called the stone. It was very important to pre-European Maori. It is an extremely hard stone, with the tensile strength of steel. Made of interwoven fibres, it will actually bend before breaking, and holds a sharp edge. So pounamu was to Maori what bronze or steel was to other civilisations, and all our finest tools were made from it.
When Captain Cook discovered New Zealand in 1769 he saw the Maori working a green coloured stone which is how the name of ‘Greenstone’ originated.