Tourmaline
Tourmalines have one of the widest colour ranges of any gem species, occurring in various shades of virtually every hue. Tourmaline’s colours have many different causes. It’s generally agreed that traces of iron, and possibly titanium, induce green and blue colours. Manganese produces reds and pinks, and possibly yellows. Some pink and yellow elbaites might owe their hues to colour centres caused by radiation, which can be natural or laboratory-induced.
