GAUDEFROYITE FROM THE KALAHARI MANGANESE FIELD, SOUTH-AFRICA

Gaudefroyite from the Wessels and Nchwaning mines in the Kalahari mang anese field, South Africa is described. The mean structural formulae v aries between Ca4Mn+32.81 [(BO3)3/(CO3)/(O2.43,OH0.57)SIGMA=3] and Ca4 Mn+32.74[(BO3)3/(CO3)/(O2.23,OH0.77)SIGMA=3] for the two localities re spectively. It has the space group P6(3) and refined unit cell paramet ers a(o)=10.5995 (+/-0.0006)angstrom, c(o)=5.8850 (+/-0.0005)angstrom, c/a =0.5552 and V=572.5956 (+/-0.0718 angstrom3 with Z=2. The ten str ongest lines in decreasing intensity (dangstrom, intensity, hkl) are 4 .59, 100 (200); 2.48, 96(202); 2.65, 85(220); 2.99, 52(211); 1.81, 47( 402); 9.18, 40(100); 2.71, 31(301); 2.34, 28(311); 1.49, 28(422) and 2 .24, 23(212). Gaudefroyite is of late secondary, hydrothermal origin b eing contemporaneously deposited with baryte during boron metasomatism .