Staurolite

Staurolite is a silicate with composition (Fe,Mg)₄Al₁₇(Si,Al)₈O₄₄(OH)₄ . This sample is about 8x9 cm and is from Monte Campione, Uri, Switzerland. The staurolite is the background material and the embedded slender crystals are kyanite . This sample is on display at the Smithsonian Museum of Natural History.