CARBON SILICA

carsil.jpg - 7648 Bytes
(from Vesuvius)

Anybody know what this is? In Italian, it's Silicio di Carbonio, thus my translation. It's quite light in weight; about hardness 6. The colour is dark grey and the thick prismatic "particles" shine like obsidian. And it is obviously of volcanic origin. I thought perhaps Ilvaite.