What causes color zoning in a gemstone?

Color zoning in a gemstone primarily arises from variations in growth conditions during its formation. As a crystal grows, it may encounter changes in environmental factors such as temperature, pressure, and the availability of various elements. These fluctuations can lead to different colors developing within the same crystal. For instance, if certain elements that impart color are more abundant at particular times during growth, that portion of the crystal may take on a distinct hue compared to other sections formed under different conditions. This phenomenon can result in striking patterns, such as bands of color or areas of dual color within the stone, which can be seen in gemstones like tourmaline and amethyst. Understanding this aspect is essential for gemologists when assessing a stone's value and beauty.