SoLLAS — On the Crystalline Form of Rieheckite. 523 



mineral and arfvedsonite, inasmuch as in the latter the iron is chiefly 

 present in the ferrous, and in the fonner in the ferric state. Konig,^ 

 however, has analysed a rieheckite in which ferrous are in excess of 

 ferric molecules ; and Brogger is disposed to consider the state of 

 oxidation of the iron as of subordinate significance compared to the 

 total quantity of this constituent present. 



Lately C. Palache' has linked on giaucophane to rieheckite by the 

 discovery of a new species of amphibole (Crossite) in which one 

 giaucophane molecule (aluminium sodium silicate) occurs in association 

 with two riebeckite molecules (ferric sodium silicate). It is a curious 

 fact, however, that while the new mineral , stands intermediate to 

 giaucophane and riebeckite as regards its chemical composition, in its 

 optical characters it departs more widely from giaucophane than does 

 riebeckite itself. 



To complete the comparison between riebeckite and arfvedsonite the 

 following Table is added : — 







Cktstallogeaphic Elements. 





Hornblende, 



a : b : c 

 . 0-54826 : 1 : 0-29377 



13 



75° 2' 



Arfedsonite, 



. 0-54957 : 1 : 0-29751 



75 41 



Riebeckite, 



. 0-54748 : 1 : 0-29246 

 Angulae Meastjeements. 



76 10 



(110) 



(110) 



HORNBLEXDE. ArFVEDSONITE. 



Calculated. 



55° 49' 56° 5' 



illEBECKITE. 

 Calculated. 



56° 



(110) 



(010) 



62 6 61 57i • 



62 



(100) 



(001) 



75 2 75 44i 



76 10' 



(110) 



(001) 



76 48 77 27 



77 50 



(111) 



(001) 



34 25 34 39i 



34 7 



(111) 



(110) 



68 47 67 53 



68 4 



(111) 



(010) 



74 14 74 7 



74 22 



(021) 



(010) 



60 26 60 2 



60 24 



^ Grote's Zeits., vol. i., p. 434. 



2 " On a Eoek from the Yioinity of Berkeley, containing a New Soda Amphi- 

 bole," by C. Palache, Bull. Depart. Geology, University of California, vol. i., 

 p. 185, 1894. 



