Which treatment is primarily used to change light-colored spodumene to kunzite?

The treatment that is primarily used to change light-colored spodumene to kunzite is irradiation. When spodumene, a pyroxene mineral, is subjected to irradiation, particularly through gamma rays or neutron radiation, the color of the stone can shift to a deeper pink or violet hue, which is characteristic of kunzite. This process creates the attractive coloration seen in kunzite, enhancing its appeal for use in jewelry.

Other methods mentioned, such as color mixing, high pressure, and natural sunlight, do not achieve the same transformative effect on spodumene. Color mixing involves blending different colors, which is not applicable to changing the inherent properties of spodumene. High pressure treatments are generally used for creating synthetic diamonds rather than altering spodumene. Natural sunlight can change some stones' color temporarily, but it does not produce the stable and vibrant coloration that irradiation does. Therefore, irradiation is the preferred and effective method for converting light-colored spodumene into the desirable kunzite stone.