334 Y. KIKTJCHI 



Fig. 10. — First stage of the alteration of Cordierite, as seen in a 

 microscopic slide taken parallel to the prismatic zone ; from the irregu- 

 lar fissures running transversely, begins the deposition of the altered 

 product forming a double layer. From these fissures, the alteration 

 proceeds along the fine canal-like clefts running in a longitudinal 

 direction, x 20. 



Fig. 11. — Microscopic view of the completely altered crystal 

 or Pinite-like pseudomorph from Tamba, cut longitudinally through 

 nearly the middle of the crystal, to show the parallel arrange- 

 ment of the mica-flakes along the base. Thick black lines and dots 

 are the interpositions of carbonaceous matter, showing the directions 

 of growth at right angles to each other, corresponding to the systems 

 of bundles in Fig. 6. The fine transverse lines are the cleavage traces 

 of the mica Hakes, x 20. 



Fig. 12. — Transverse section of the crystal through its middle 

 portion. The three individuals which make up the twin along 

 (110) are widely separated from each other, due to the development 

 of the maeropiuacoidal faces (100). x5. 



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