Which gem is frequently subjected to heat treatment?

Heat treatment is a common practice in the gemstone industry to enhance the color and clarity of certain gemstones. Sapphires are particularly well-known for frequently undergoing this process. Heat treatment in sapphires can improve their color vibrancy and remove inclusions, making them more appealing to buyers. This process is widely accepted and often expected, resulting in a significant improvement in the stone's marketability.

While topaz and emeralds can also be treated, the extent to which sapphires are commonly enhanced through heat treatment outpaces the other gemstones listed. Amber does not typically require heat treatment, as its natural beauty is often sufficient without enhancements. Thus, sapphires stand out as the gemstone most frequently subjected to heat treatment in the colored stone market.