Gem (Tree) Rings
Liddicoatite — named after GIA’s former president Richard Liddicoat (he created the International Diamond Grading System™) — is a rare species of tourmaline that shows a distinctive triangular pattern, often with a three-rayed star, when its rod-shaped crystal is sliced horizontally. These bands of color reveal the crystal's history, similar to how the rings of a tree record the tree's past. The colors of the gem changed over time, because the solution that fed the crystal's growth contained different elements as the crystal grew. Manganese could cause the gem to turn purple while iron could cause the gem to turn yellow.