Which property can supply information about a gem's chemical composition?

• A. Luster
• B. Specific Gravity
• C. Absorption Spectrum
• D. Hardness

Answer: (C)

Absorption spectroscopy directly reveals what elements are present in a gem. When light passes through or reflects from a gemstone, electrons absorb energy at specific wavelengths corresponding to transitions between their atomic or ionic energy levels. Those absorptions occur at characteristic wavelengths for particular elements, so the resulting spectrum serves as a fingerprint of which elements are in the gemstone and, to some extent, their relative amounts. By studying the absorption spectrum, you can identify the chemical species inside the gem and detect trace impurities that influence color and identity. This is why the absorption spectrum is the go-to tool for inferring composition.

Luster describes surface light reflection, not chemistry. Specific gravity relates to density and can hint at composition in a broad sense but doesn’t provide a direct chemical readout. Hardness reflects bonding and crystal structure, not the exact elements present.