SOME OCCUEKENCES OP PIEDMONTITE IN JAPAN. 305 



Piedmontite. 



Crystalsî of Piedmontite are usually much elongated, traversed, 

 by transversal irregular cracks and fissures, and sometimes broken, 

 when the dismembered parts form chains with faces striated in the 

 direction of the axis of symmetry (ortho-axis); and nearly all the 

 crystals lie with the supposed orthopinacoid (oo P^), parallel to the 

 plane of schistosity of the rock. 



In contrast to common rock-forming Epidote in which the well- 

 defined crystallographic forms are seldom to be observed, the crystal- 

 individuals have here usually well-developed faces of M {o P), 

 T (oo P 5i5), {( i P go), r (P ^) and n ( P). (Pig. II). 



The vicinal section of the clinopinacoid (co P cb ) is, as a rule, of 

 a rhomboidal outline, caused by the predominance of the traces of 

 T and i (Pig. Ill); and, if the face M in at the same time well- 

 developed, the section will be the six-sided. This latter case is how- 

 ever of less frequent occurrence. In common Epidote the face r (P^) 

 is said to be a predominating element, and, as a rule, it is more perfect 

 than the face T (oo Pco).(') In our Piedmontite, the face 7* is very 

 poorly developed, and is commonly not visible even in the clino- 

 pinacoidal section ( Pig. III). Outlines of the clinopinacoidal section 

 are never regular, owing to the fact that there are an infinite number 

 of prominences and indentations. They are sometimes even knee- 

 shaped, just like twins of Rutile. 



All these facts are due to the parallel growth and intergrowth 

 ("laterale Juxtaposition und Umwachsung") of two or more indivi- 

 duals of different size; and the striations commonly observed on the 

 faces parallel to the orthoaxis arise mainly from these causes, and 

 comparatively few stripes are assignable to the formation of twins. 



(i) Rosenbuscli, 'Mikroskopische Physiographie,' I Baud, 2te Auflage, p. 496. 



