Sardonyx

Sardonyx is an Agate that is a mixture of the patterning of Carnelian or Sard, and Onyx, so it has red brown base colouring with either black or white stripes. It is fairly hard to find naturally now, there has been a lot of 'Sardonyx' for sale in the last few years reportedly from Madagascar, that is in fact grey banded Agate that has been treated in a number of ways, including acid and sugar heat treated, to darken it and create red, black and white banding. When these stones are cut open the true grey colour of the Agate is revealed. Sardonyx was particularly popular with the Romans, as the banded layers allowed them to carve the popular cameos and intaglios in different colours.