During the 'sorting-out' stage of gem testing, which property is among those generally most useful?

• A. Refractive Index
• B. Specific Gravity
• C. Color
• D. Fluorescence

Answer: (A)

Measuring the refractive index provides a quick, reliable first filter in the sorting-out phase because it’s a fundamental optical property that can be obtained with a simple, non-destructive test. The refractive index gives you a numeric value that narrows the field to a short list of likely minerals. Many common gemstones fall into distinct RI ranges (for example, quartz around 1.54–1.55, topaz about 1.62–1.63, corundum near 1.76–1.77, and diamond around 2.42), so you can rapidly separate out wide classes and move on with more targeted tests. This makes RI the most broadly useful initial discriminator.

Specific gravity can help but takes extra time and care, often requiring immersion liquids and precise measurements; it’s also influenced by inclusions or mounting materials. Color is highly variable and can be altered by treatments, so it’s not dependable for a first sorting. Fluorescence depends on the light source and can be inconsistent, providing valuable clues only in certain cases.