Staurolite

Staurolite is a mineral known for its distinctive cross-shaped crystals, often called "fairy crosses" or "cruciforms." It forms in metamorphic rocks like schists and gneisses under high temperature and pressure conditions. Its characteristic twinned crystals typically appear as cross-like shapes, measuring a few millimeters to centimeters. The mineral has a reddish-brown to black color and a glassy luster. Staurolite is valuable to collectors and helps geologists identify certain metamorphic environments, providing insights into the geological history of the rocks where it occurs.