(obsianus lapis, 'stone of Obsius'; obsidianus is the incorrect reading) is a dark, vitreous (Plin. HN 36,196: in genere vitri = Isid. Orig. 16,16,5) volcanic rock that a certain Obsius of Ethiopia is said to have imported to Rome.
In the Near East, obsidian was highly regarded from the 8th millennium and in Egypt from the 4th millennium, principally because of the sharp cutting edges of tools that were made of obsidian blades but also because its semi-transparent property made it attractive as a gemstone (Akkadian ṣurru; Egyptian mnw). From the 2nd millennium, obsid…