480 



ON OCCURRENCES OF PIEDMONTITE-SCHIST IN JAPAN. 



vitreous grains of quartz, are all thrown together within the garnet 

 crystal, these enclosures assuming a more or less curved course. 



The colour of the garnet itself is deep yellow, and the crystals 

 show anomalous optical properties, being anisotropic. This is 



Fig. 5. 



(.--■:- .••.'•** s. .'■ 4 y-' '«.-,' \A v a,- ' 



caused probably by the strain from the interposition of other minerals 

 contained in it. Prof. Bonney* has also found garnet in cer- 

 tain glaucopbane-bearing rocks near Berrioz, Yal d'Aoste, in the 

 Alps. Here the garnet sometimes contains glaucophane and dark 

 dust (?), which he suggests may be possibly due in certain cases to 

 subsequent infiltrations. The garnet here described is entirely free 

 from enclosures of glaucophane, although the rock itself is a glauco- 

 phane-schist ; and the above-mentioned interpositions, i. e. pied- 

 montite, &c, seem to have been developed prior to, or contem- 

 poraneously with, the formation of the garnet. 



Discussion. 



The President remarked that, in the slides, where the glauco- 

 phane was best developed, there the piechnontite was most rare, and 

 that where the piechnontite was abundant but little glaucophane 

 was to be seen. He alluded to the striking pleochroism of the 

 piedmontite, and to the interesting fact of its having been now 

 recognized for the first time as a rock-constituent. 



Mr. Mters, whilst claiming but little special knowledge of the 

 minerals described, expressed his satisfaction with the paper. 



Mr. Hudleston said that the President's remark precisely con- 

 firmed Mr. Koto's statement to the effect that the piedmontite exists 

 only as an accessor}^ mineral in the glaucophane-rock, whilst it is 

 one of the principal constituents in the piedmontite-schist, which 

 contains hardly any glaucophane. 



* " On a Glaucophane-eclogite from the Val d'Aoste," Min. Mag. vol. vii. 

 no. 32, p. 2 (1886). 



