What instrument is commonly used to detect pleochroism in stones like sapphire and emerald?

• A. Spectroscope
• B. Dichroscope
• C. Refractometer
• D. Polarimeter

Answer: (B)

Pleochroism is the phenomenon where a gem shows different colors when viewed from different crystallographic directions because the crystal absorbs light differently along those directions. The dichroscope is used to detect this because it splits light into two rays that travel along two different vibration directions. By looking through the device, you can see two colors side by side if pleochroism is present, which is common in stones like sapphire and emerald. The other instruments serve different purposes: a spectroscope reveals an absorption spectrum, not directional color changes; a refractometer measures refractive indices; a polarimeter gauges optical rotation. So the dichroscope is the best tool for revealing pleochroism.