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Published online by Cambridge University Press: 14 March 2018
The continuation of the mapping of the aureole of metamorphism round the Bodmin Moor granite has led to the discovery of fresh occurrences of idocrase, developed in the altered, impure limestones. The failure to find this mineral hitherto is now clearly due to the former absence of artificial openings in suitable localities, for the mineral has so far not been found in recognizable form in natural exposures, owing to the rapidity with which these calcareous rocks decompose.
Altered calcareous rocks containing idocrase in considerable abundance have recently been laid open in a small quarry on the west side of the stream at Tvenuth Mill, which is about 400 yards south of the granite margin in the well-known Caradon area.
Communicated by permission of the Director of H.M. Geological Survey. Compare G. Barrow and H. H. Thomas, ‘On the occurrence of metamorphic minerals in calcareous rocks in the Bodmin and Camelford areas, Cornwall.’ Min. Mag., 1908, vol. xv, pp. 113-123.