A new review of the chlorites

Abstract

The chlorites form an extensive isostructural series with a high degree of isomorphous substitution, within which it has always been difficult to define or delimit species; until recently, owing to the lack of adequate X-ray studies; several structurally distinct species were included with the group, further complicating the problem. The group comprises aluminosilicates of magnesium and iron (ferrous and ferric); a few contain appreciable amounts of chromium, nickel, or manganese, and one (pennantite) contains manganese as a major constituent. The first step towards the understanding of the relations of the chlorites was taken by G. Tschermak (1890, 1891), who divided them into two groups: the orthochlorites, with compositions between (Mg,Fe")2 Al 2 SiO 5(OH)4 and (Mg,Fe")2 Si 2 O 5(OH)4, and the leptochlorites, with compositions not explicable on this basis, and in general richer in trivalent ions (often including considerable Fe"′) relative to silicon and divalent ions. The two orthochlorite end-members have the composition of amesite and serpentine respectively, but it is now known that neither of these two minerals has the chlorite structure.