Liddicoatite. Slice from a single crystal of liddicoatite. The colour-zoning reveal the crystal's history, just as the rings in a tree records its past. Crystals may start and stop growing many times. In most cases, there is no way of knowing how long each phase lasted. This particular crystal changed color as it grew. The pink portion of the liddicoatite formed when the solution feeding it was manganese rich. The green part grew when the solution became iron rich.
The Dynamic Earth @ National Museum of Natural History