Color origin cannot currently be determined.
Many gemstones are routinely treated by different methods to improve the color or appearance. In some cases, treatments like heating and irradiation cannot be detected.
Heat treatment
A wide range of gem materials may be subjected to low temperature heat treatment to improve or change the color of the stone. It is also possible for this heating process to occur naturally when the gemstone is in the earth. To determine if the heating was done artificially as a treatment or heating by nature may be difficult if not impossible with today’s testing methods.
Irradiation
Some gem materials may be subjected to irradiation to improve or change the color of the stone. Generally, there is no residual radioactivity left in such stones. These same gemstones may be naturally irradiated in the earth over a long period of time. To determine if the irradiation was done artificially as a treatment or heating by nature may be difficult if not impossible with today’s testing methods.
The list below contains those gem materials that may be subjected to heating or irradiation. The frequency of these treatments for any given material ranges from occasionally—red tourmaline—to almost always—tanzanite. This isn’t intended to be a comprehensive list. Other gemstones might also be treated but these are the most significant.
Diffusion treatment
In yellow and/or orange sapphires it is not possible to dismiss diffusion treatment.
| Species | Variety/Color | Heat | Irradiation | |
| Beryl | Aquamarine | x | ||
| Morganite | x | or | x | |
| Golden | x | or | x | |
| Heliodor | x | |||
| Green | x | or | x | |
| Quartz | Citrine | x | or | x |
| Smoky | x | |||
| Prasiolite | x | or | x | |
| Topaz | Blue | x | ||
| Brown | x | |||
| Imperial | x | |||
| Tourmaline | Pink to red | x | ||
| Blue | x | or | x | |
| Green | x | or | x | |
| Paraiba | x | |||
| Spodumene | Kunzite | x | ||
| Zircon | Blue | x | ||
| Colorless | x | |||
| Red | x | |||
| Zoisite | Tanzanite | x | ||
| Fluorite | Blue | x | ||
| Apatite | Blue | x | ||
| Diamond | Black | x |
