Glaucophane, along with the closely related mineral riebeckite, to which it forms a series with, and their intermediate crossite, are the only well known amphiboles that are commonly blue. Glaucophane forms a solid solution series with ferroglaucophane (Na2(Fe,Mg)3Al2Si8O22(OH)2). Glaucophane is the magnesium-rich endmember and ferroglaucophane is the iron-rich endmember.