Ametrine

    Ametrine is a variety of quartz that contains both amethyst and citrine sectors in the same crystal. Both amethyst and citrine are colored by small amounts of iron (approx. 40 parts per million). Amethyst color develops when iron-containing quartz is exposed to ionizing radiation. In nature, gamma rays from the decay of potassium-40 are the most likely source of ionizing radiation. The model currently accepted is that radiation oxidizes Fe³⁺ to Fe⁴⁺. There is still uncertainty about the site of the iron. Both interstitial sites in the c-axis channels, and the silicon tetrahedral sites have been proposed as the site of the amethyst center. Citrine color is from Fe³⁺. The properties of the Fe³⁺ spectra suggest that the Fe³⁺ ions are aggregated and hydrated in clusters of unknown size.

Serendipity Ranch Gem Mine