Which statement best describes an absorption spectrum in gems?

• A. A pattern of dark vertical lines or bands shown by certain gems when viewed through a spectroscope, or a linear graph recorded by a spectrometer.
• B. A measure of brightness of a gem under standard lighting.
• C. Energy difference between the valence band and the conduction band.
• D. Emission of visible light during stimulation by UV or X-ray radiation.

Answer: (A)

An absorption spectrum shows dark lines where the gem absorbs specific wavelengths of light as white light passes through it. When light is dispersed and analyzed, the material’s atoms and trace elements take out certain colors, so those wavelengths disappear from the transmitted light. A spectroscope or spectrometer would reveal dark lines or bands at the absorbed wavelengths. This differs from simply measuring how bright a gem appears, which doesn’t reveal which wavelengths are being absorbed. It also contrasts with fluorescence, where emission of light occurs under UV or X-ray stimulation. The absorption pattern serves as a spectral fingerprint of the gem’s composition and explains why the stone’s visible color arises from the remaining wavelengths.