Bustamite, rhodonite, spessartine, and tephroite from

Summary. Chemical analyses together with optical and physical properties are given for ferroan bustamite, rhodonite, spessartine, spessartine-grossular, and tephroite from contact metamorphosed ale-silicate rocks of the Meldon Railway Quarry, Okehampton. The compositions of these minerals are compared to those from the Treburland manganese mine, Cornwall. An analysis is also given of a spessartine from ~ pyrrhotite-spessartine skarn rock from the nearby Meldon aplite quarry. C ONTACT metamorphism and metasomatism by the Dartmoor granite on the Calcareous Group of the Lower Cuhn (Lower Car-boniferous) sediments of the Meldon district, south-west of Okehampton, Devonshire, has given rise to banded eale-flintas which locally have been converted to coarse eale-silieate hornfelses with the introduction of sulphur, fluorine, boron, iron, and manganese. In the basal bed of the Calcareous Group, in the core of an anticline exposed in one of the high-level quarries at the southernmost end of the British Railways Quarry complex, there is a small occurrence of manganiferous silicates, described briefly by Dearman and Butcher (1959) and by Dearman (1962). This assemblage has now been examined in more detail and is seen to include coarse radiating crystals of brown bustamite (fig. 1) often closely associated with pyrrhotite, together with relatively more massive pink rhodonite, with local development of tephroite and small (2-3 mm) golden yellow spessartine garnets. Quartz occurs patchily, and the black secondary oxidation products typically found with most manganese-rich assemblages are also present on joints and cracks: although rhodo-ehrosite has been recorded it is not very abundant. In mineralogy and paragenesis the Meldon Railway Quarry assemblage is reminiscent of that of the old Treburland manganese mine in slate or phyllite a few hundred yards from the Bodmin Moor granite south of Altarnun, Cornwall: rhodonite and tephroite from ~his latter locality have been described by Russell (1946) and the bustamite from Treburland has been described by Tilley (1946)