Elements present in a mineral in minor proportions (between 0.1-2.0%) but which are frequently characteristic of the original source of the material. Trace elements occur naturally in minerals in soils and sediment and are not added deliberately to a substance. Minute amounts of chemical elements found in minerals emit characteristic wavelengths of light when heated to incandescence. Quantitative analyses of metal, clay, obsidian, etc. can show the amounts of the trace elements present and may suggest a source. Source identification can lead to further interpretations of trade and economic systems.