Abstract: The Outokumpu region of Finland is notable for the large number of Cr-rich silicate and oxide phases associated with the massive sulphide deposits. In this paper analyses of Cr-rich phases in the epidote-clinozoisite and muscovite groups are presented. The muscovite-type phase shows a maximum 80% substitution of Cr for A1 on octahedral sites with a maximum 24.7 wt.% Cr₂O₃. Apparent complete solid solution between this extreme composition and the fuchsitic muscovites is indicated. The clinozoisite type phase has a maximum 15.4 wt.% Cr₂O₃, with a composition close to Ca₂CrAl₂Si₃O₁₂(OH). As with the micas, complete solid solution of Cr for Al in the clinozoisite structure is indicated.