OBSIDIANUS LAPIS, in the natural history of the ancients, the name of a stone which they have also described under the name of the Chian marble. It is a very smooth and hard marble, extremely difficult to cut, but capable of a fine polish; and was used among the ancient Greeks for the purpose of making reflecting mirrors. The later writers have supposed
the name obsidianus to be derived from somebody called Obsidius, who was the inventor of this use of it; but it seems only a false spelling of the word opsidianus, απο της οψιδ, from seeing the images of things in it.