a grey or violet-blue dichroic mineral that consists of magnesium aluminium iron silicate in orthorhombic crystalline form and is found in metamorphic rocks. Formula: (Mg,Fe)2AL4Si5O18.nH2O
Also called: dichroite, iolite
Word origin
C19: named after Pierre L. A. Cordier (1777–1861), French geologist who described it