Which property is most useful for initial separation of gems based on density?

• A. Absorption Spectrum
• B. Specific Gravity
• C. Refractive Index
• D. Luster

Answer: (B)

Specific gravity is the best fit for initial separation by density because it directly measures how heavy a gem is for its size relative to water. By comparing a gem’s weight in air to its weight when submerged in a known liquid, you get a quick density estimate (float or sink) that lets you group stones into density ranges right away. This early sorting is exactly what density-based separation aims to achieve, narrowing down the possibilities before more detailed testing. Other properties—absorption spectrum, refractive index, and luster—relate to color, how light bends, or surface appearance, none of which provide a direct measure of density, so they aren’t useful for this initial step. Remember that factors like inclusions or porosity can tweak SG, but it remains the practical first-screen tool for density-based grouping.