(Al,Fe)₇(SiO₄)₃(BO₃)O₃

This sample of Dumortierite is displayed in the Smithsonian Museum of Natural History. Dumortierite is a silicate with boron , or a borosilicate, with the composition (Al,Fe)₇(SiO₄)₃(BO₃)O₃ . This sample is about 15x20 cm and is from Dehesa, California.