The chemical composition of xonotlite and associated inesite from the Nchwaning and Wessels mines, Kalahari manganese field, South Africa

The chemical composition of xonotlite and inesite differs between (Ca5.94Fe0.03Mn0.02Mg0.01)(Sigma) (=) 6.0Si6O17(OH)(2) and (Ca1.77Mg0.23)(Sigma = 2.00)(Mn6.94Fe0.03) (Sigma =) 6.97Si10O28(OH)(2). 5.01H(2)O for occurrences at the Nchwaning mine and (Ca-5.90 Fe0.06Mn0.02Mg0.01)(Sigma) = 5.99Si6O17(OH)(2) and (Ca1.91Mg0.09)(Sigma) (=) (2).(00)(Mn6.92Fe0.06)(Sigma) (= 6.98) Si10O28(OH)(2) 5.01H(2)O for samples from the Wessels mine in the Kalahari manganese field, South Africa. Both xonotlite and inesite are of late stage, relatively low temperature hydrothermal origin and occur as white and flesh coloured radiating fibres, respectively. The presence of datolite in these samples is indicative of boron metasomatism. The Wessels mine is situated near to a postulated regional thrust fault along which aqueous fluids could have migrated during metamorphism, while the Nchwaning mine is not associated with major deformational structures. The compositional contrast between the two sites probably reflects a thermal gradient during metamorphism.