Abstract

A transmission electron microscopy (TEM) study of gaudefroyite,

\(Ca_{8}Mn_{6}^{3+}[(BO_{3})_{6}(CO_{3})_{2}O_{6}]\)
, from the Wessels mine, Kalahari manganese field, South Africa, shows strong, continuous streaking in selected-area electron diffraction (SAED) patterns. The pseudo-hexagonal parameters for gaudefroyite are a = 10.606(1) and c = 5.896(1) Å. The symmetry of gaudefroyite is lower than hexagonal because of the streaked reflections. The CO3 groups in the large 63 channels are ordered in two different ways and this ordering gives rise to two different types of channels, A and B. The A and B channels occur in a 1:1 ratio and these channels are partially ordered and give rise to the continuous streak reflections in gaudefroyite.

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