Dislocations in orthorhombic minerals. Part 1.—Naturally-occurring barytes

Abstract

The emergence points of dislocations at cleavage faces of natural barytes crystals have been identified using the etchpit technique. The alignments of these etchpits and the observation of slip traces both in as-grown and deliberately deformed crystals yield the active slip planes in this material. The results compare favourably with a recent independent study of natural barytes crystals employing the X-ray topographical technique. Comparisons are made between barytes and the isomorphous ammonium perchlorate. It is found that, with one notable exception, the dislocation structures of these two materials are identical and probably characteristic of the space group, Pnma. The slip systems are {201}[101]; {401}[010]; {110}〈110〉; {001}[010]; {010}[001]; {101}〈101〉 or {101}[010], {110}[001] and {201}[001], the last-named being active in barytes only. The important criterion when considering the γ-irradiation behaviour of these two materials is the thermal stability of the respective lattices.