 During their growth, these tourmaline crystals incorporated Mn2+ and were initially very pale.Due to natural gamma ray exposure from radioactive decay of 40K in their granitic environment, gradual formation of Mn3+ ions occurs, which is responsible for the deepening of the pink to red color.Opaque black schorl and yellow tsilaisite are idiochromatic tourmaline species that have high magnetic susceptibilities due to high concentrations of iron and manganese respectively.