OBSIDIAN ( from Lat. obsirfiuna, false read ing for obstana, a sort of mineral, probably ob sidian, from nbsidius, false reading for (Asius, name 4 if a man who is said to discovered it in Ethiopia). A glass consisting of silica in combination with aluminum, calcium. iron. potassium, and sodium. It is hard and brittle, with a remarkable vitreous lustre. and in•rfect eonehoidal fracture, the edges of the fracture. which are semi transparent or trans lucent, being very -harp and cutting like glass. Olisi Ilan is generally black or very dark gray, but sometimes has a green. red, or brown color, i• griped or spotted, and even ehatoyant or aventurine. It occurs in volcanic regions, in round compact pieces. granular or fibrous. It is often found in association with pumice, which is identical with it in chemical composition. but different in structure. Pitch-tone is also of similar composition. but contains a larger per centage of water and is without lustre. Obsidian
is found in the volcanic regi s of lei-land. Itabs. IInugary. Spain. New Zealand, Siberia. Mexico. Peru. and the western parts of the I "Ili ted States, especially in Georgetown, Col., and at the Obsidian Cliff in the Yellowstone Park, where it occurs in massive form. The famous locality in Mexico is the Cerro de Navajas, or 'I 1 i I 1 of Knives,' in the State of Alichoacan. Obsidian takes a high polish. but is very brittle. Nevertheless, it was extensively used among primitive peoples for arrowheads and spearheads, for knives, mirrors. polished figures. and orna ments. the best specimens of which have been found in .Nfexico. The early Romans obtained obsidian mirrors from Ethiopia. The mineral is still 'sometimes employed as material for orna mental boxes, button-, and other articles