Bracelet with geometric decoration

Wide, cylindrical ring with slightly concave walls, possibly a bracelet; translucent, very pale greenish gray with cloudy veinings and a dark brown area partly covering one rim, sprinkled with incipient disintegration; decoration: incised and in very low relief, lozenge-pattern borders enclose band of continuous, geometric design; earth incrustations on interior. (One long crack and some recent chips and scratches.)