On some Occurrences of Piedmontite-Schist in Japan

Abstract

As already stated in a former paper, the occurrence of manganepidote or piedmontite is often associated with glaucophane-bearing rocks in the crystalline-schist system in Japan. The rock which contains piedmontite as an essential component is well characterized in outward appearance, being of a dark violet colour; hence it is locally named the ‘murasaki’ or violet rock, and it is most typically developed in the Island of Sikoku, especially in the neighbourhood of the city of Tokusima. The first specimen that came under my notice was brought from Mount Otakisan, one mile to the south-west of the last-named city; and many localities have since been added to the list of places where it occurs, so that we are now able to trace out the geological horizon of the piedmontite-bearing rock everywhere within the crystalline-schist system of that island. The rock is, however, not exclusively confined to this region. It also has a wide distribution in the provinces of Musasi and Kozuké, on the main island, Honsiû. The piedmontite is associated with fine quartz-grains; and by the parallel position of the former, the rock itself assumes a schistose structure, a vertical section presenting a regularly banded appearance resulting from the alternation of fine piedmontite layers with those of quartz. The accessory components are muscovite (hydrous mica of Prof. Bonney†), greenish-yellow garnet, rutile, some felspars (probably orthoclase), blood-red iron-glance, and also opaque crystals of the same mineral. This is the typical piedmontite-sehist. In the glaucophane-bearing rocks‡ manganepidote also makes its appearance, but it