In this study, the red corundum, Al1.90Cr.02O3, from Froland is characterized structurally and compositionally. The crystal structure has been refined from X-ray (CuKa?1) powder diffraction data. Space group 3? c Z = 6, a= 4.7597( 4) Å, c = 13.0013(9) Å. The substituting Cr-atoms do not take the site of Al-atoms, they depart 1.04 Å in the direction of the vacant octahedral interstices. A SEM ( EDS) study revealed microphases of diaspore; one of the reasons for gem quality beeing lost. The result suggests that the reaction Al2O3 (Cm)+ H2O = 2AlO(0H) (Dsp) occurred in the late stage of the metamorphic htstory of the Froland region.
B. Estifanos, P. G. Andreasson, G. Bylund and L. Johansson, Department of Geology, University of Lund, Solvegatan 13, S-223 62 Lund, Sweden;
K. Ståhl, Inorganic Chemistry 2, University of Lund, P.O. Box 124, S-221 00 Lund, Sweden.