Vol. 4] 



Murgoci. — Classification of the Amphiboles. 



371 



v These amphiboles are optically related to crocidolite ; the cro- 

 cidolite is related, optically and chemically, to arfvedsonite and 

 riebeckite on one side, to rhodnsite, and to glancophane on the 

 other side. 



Another similar blue fibrous amphibole in the quartz from 

 Oak Ridge, California, is very probably crossite; the optical 

 orientation (the = -17°) and pleochroism are identical with 

 crossite. 



Pig. 3. — Stereographic projection on (010) of the optical orientation of 



Relation between optical properties and chemical composition 

 in the glancophane series. — Comparing the analyses of the am- 

 phiboles from the glancophane series (Table I), we see that Na 2 0, 

 FeO, and MgO undergo little or no variation, while A1 2 3 and 

 Fe 2 :i show variation in opposite directions. 



(a). The intensity of color and pleochroism (absorption) are 

 not due only to the amount of Na.,0 (or Na 2 Si0 3 ), because the 

 glaucophanes of Zermatt, Syra, San Pablo, etc., are very differ- 

 ent in their absorption, and still have almost the same amount of 

 Na 2 0. Very probably the Na 2 Si0 3 determines the shade of the 

 color, but not the intensity. 



A. Lacroix* has emphasized the fact that the glaucophanes 

 rich in iron have more intense colors; Broggerf states too that 

 amphiboles rich in iron (but without Ti) are blue. The accom- 

 panying analyses verify these statements in respect to Fe 2 3 . 

 The amount of FeO, however, seems to have no influence on the 



* A. Lacroix, Mineralogie de la France, p. 700. 



t W. C. Brogger, Eruptivgesteine des Kristiania Gebiet, I, 37. 



0„ Cd 



common crocidolite, Cd., with normal axial and osannite, Os. 



