Forty samples of obsidian from Ecuador, both archaeological artifacts and unworked samples, were analyzed by high-precision neutron activation analysis and by x-ray fluorescence. Six chemical composition patterns could be distinguished. One artifact matched a primary source known as Mullumica, another a secondary source known as Rodeo Corrales. The origins of the other groups are still unknown. The Mullumica source is variable in composition, and some of the unidentified chemical groups may actually derive from this source. See 18-1022. -- AATA