III. Ox TIIK ClIONDUODITE FROM Till': Tll,I,Y-F()STKK IkOX MlNK, 



BuKWSTKR, Kkw York. By Edward S. Dana. 



WITH THREE PLATES. 



The interesting discovery by Seacchi,* of the existence of three 

 types in the crystals of the Yesnvian huniite, gives especial interest to 

 the study of chondrodite — a mineral identical with humite in chemi- 

 cal composition, and yet very diiferent in appearance, as well as in 

 origin and method of occurrence. The same subject of humite has 

 since been more exhaustively investigated by vom Kath,f with the 

 entire confirmation of Scacchi's views. These authors have shown that 

 the crystals of humite are to be divided into three groups, all bear- 

 ing the same relation to each other in respect to their lateral axes, 

 while the vertical axis has a distinct value for each type. In other 

 words, the planes occurring upon a given crystal bear simple relations 

 to each other, whereas only very complex symbols result when the 

 planes of one type are referred to the axes of another. For a full 

 explanation of this subject reference must be made to the valuable 

 memoirs al)ove alluded to. It will be sufficient to give as an example 

 the symbols of the occurring pyramids of the r series on the second 

 and third types of chondrodite (see beyond) ; (1) as referred to their 

 own axes ; (2) as referred to the axes of the second type. 



* rogg. Ann.. Erg. Bd. iii, 161, 1851. 



f Pogg. Ann., Erg. Bd. v, 321, 1871 ; vi, 385, 1873. 



