Mg₄Al₆(Si,Al,B)₅O₂₁(OH)

This sample of kornerupine is displayed in the Smithsonian Museum of Natural History. Kornerupine is a silicate mineral which contains boron as well as aluminum and magnesium. It has the composition Mg₄Al₆(Si,Al,B)₅O₂₁(OH). The sample at left is about 12 cm across and is from Oure Mississippi, Fiskernies district, Greenland.