Which gemstone is considered a result of heat treatment from another stone?

Citrine is considered a result of heat treatment from another stone, specifically amethyst. In the gemological process, natural amethyst can undergo heat treatment to turn into citrine, which enhances its yellow to golden coloration. This transformation occurs because the heat alters the iron impurities within amethyst, changing its colors and rendering it suitable for use as citrine.

While natural sapphire is prized for its color and is not typically treated this way, amethyst itself serves as the starting material that undergoes heat treatment to achieve citrine. Blue topaz, while it may also be treated to enhance color, is not derived from heat-treated stones in the context of this question. Instead, it is often the product of irradiation followed by heat treatment, which differs from the transformation of amethyst to citrine.

This understanding of how citrine is produced helps clarify the relationship between these gemstones, particularly how one can evolve through enhancement treatments.