330 Y. KIKTJCHI. 



usually known as Finite. The addition of potash was explained hy 

 Gr. Bischof* as due to the action of circulating water containing in 

 solution, the alkaline silicates which had been derived from the 

 decomposition of granitic rocks. With this addition of potash there 

 is usually a diminution of magnesia. But in the present case this loss 

 is slight compared with the addition of potash. The amount of water 

 is also a little less than is obtained for other Pinitcs. 



From the foregoing descriptions it will be seen that Cordierite, 

 as a product of contact metamorphism, presents many peculiarities 

 which have been hitherto unobserved. These anomalous characteris- 

 tics may be accounted for by the fact that the same mineral may assume 

 different aspects according to peculiar conditions in which it was 

 formed. This is well exemplified in case of Andalusite and Chiastolite. 

 The latter is always found in the slate near the granitic contact, and 

 is distinguished from the former by the well-known cross-inclusion 

 of foreign matter, which seems to have been taken up during its 

 growth, and by the absence or weakness of pleochroism. As this 

 diagnostic difference has an important bearing upon the genesis 

 of the crystal, it would be appropriate to emphasize the name of 

 Chiastolite, so as to <nve it a signification distinct from that im- 

 plied by Andalusite, notwithstanding the fact that both are physical- 

 ly and chemically identical. It would, in fact, be best interpreted as a 

 spccijic title, according to G. Tschermak's ** definition. 



The comparison which we have drawn is likely to be true also of 

 Cordierite, since in the Japanese occurrence we have discovered its 

 second modification or species, appearing in form and con- 

 ditions analogous to those observed in Chiastolite. If, therefore, 



* Lehrbuch der chemischen vi. physikalischen. Geologie, 2te. Aufl., Bd. II, p. 579. 

 ** Lehrbuch der Mineralogie, 2te. Aufl., p. 313. 



