474 



PROF. B. KOTO ON OCCURRENCES OF 



34. On some Occurrences of Piedmontite-Scuist in Japan. By 

 Prof. Bundjiro Koto, Ph.D. (Read June 8, 1887.) 



[Communicated by Frank Kutley, Esq., F.G.S.] 



As already stated in a former paper *, the occurrence of mangan- 

 epidote 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 6 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 Kozuke, on the main island, Honsiu. 



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 mnscovite (hydrous mica of Prof. 

 Bonney t), 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-schist. In the 

 glaucophane-bearing rocks t manganepidote also makes its appear- 

 ance, but it is subordinate in quantity to glaucophane, and its 

 place is often supplied by common yellowish-green epidote. We 

 shall, first of all, speak of the epidote in the piedmontite-schist. 



(a) Piedmontite. — Crystals of piedmontite are usually much 

 elongated, traversed by transverse irregular cracks and fissures, 

 sometimes broken, and then the dismembered parts form chains, 

 with faces striated in the direction of the axis of symmetry. Nearly 



all the crystals lie with the orthopinacoid ( ooPoo ), parallel to the 

 planes of schistosity of the rock. 



Unlike the common rock-forming epidote, in which well-defined 

 crystallographic forms are seldom to be seen, these crystals of pied- 

 montite have usually well-developed faces of M (oP), T ( 00P60 ), 

 ?(|-P<^ ) ?i(P), sometimes r(P66 ) as in fig. 1. 



The clinopinacoidal section ( ooPoo ) is, as a rule, of an oblique 



* Journal of Sicence College, Imperial University, vol. i. part 1, p. 85, 

 TokyS. 



t Min. Mag. vol. vii. no. 32, July 1886, p. 3. } Loc. cit p. 86. 



