Which optical property primarily causes a diamond's fire?

• A. Dispersion
• B. Brilliance
• C. Clarity
• D. Fluorescence

Answer: (A)

Dispersion is the property that separates white light into spectral colors. As light enters and exits a well-cut diamond, different wavelengths bend by different amounts, so blue light refracts more than red. This separation of colors inside the diamond produces the colorful flashes you see—its fire. Brilliance describes the overall brightness from light return and contributes to sparkle, but it’s not what creates the color flashes. Clarity relates to internal imperfections and doesn’t cause color effects. Fluorescence can make a diamond glow under UV light, sometimes altering appearance, but it isn’t the primary source of fire in typical lighting.