94 NEW YORK STATE MUSEUM 



Pectolite HNaCa 2 (Si0 3 ) 3 



Pectolite is a silicate of sodium and calcium, and contains 

 water. 



It usually occurs in radiated aggregates of needlelike crystals 

 which are rarely terminated (pi. 7-J. Monoclinic crystals are 

 rare. The luster is vitreous to silky and the color white or 

 gray. 



Pectolite is found associated with the zeolites and prehnite in 

 cavities and seams of basic eruptive rocks. 



Rhodonite MnSiO, ^ 



Rhodonite is a silicate of manganese with part of the 

 manganese replaced by iron, calcium or zinc. 



The crystals of rhodonite are triclinic, tabular parallel to the 

 basal pinacoid, or in forms resembling pyroxene in habit but 

 with rounded edges and angles. It also occurs in cleavable to 

 compact masses and in embedded grains. The luster is vitreous 

 and the color commonly brownish red, flesh-red or pink, less 

 frequently greenish or yellowish. 



Rhodonite occurs in the United States in Maine and Massa- 

 chusetts and abundantly in the vicinity of Franklin N. J. 



Ampiribole group 



This group of minerals is closely allied to the pyroxenes, 

 forming as it does a series whose members are chemically 

 analagous to the corresponding members of a parallel series 

 in the pyroxene group. The two groups are also closely related 

 crystallographically; thus a comparison of the axial ratios of 

 pyroxene and amphibole brings out the fact that if the a and c 

 unit intercepts for amphibole be multiplied by 2 the result will 

 approximate very closely the actual values of the correspond- 

 ing intercepts for pyroxene: 



PYROXENE AMPHIBOLE AMPHIBOLE 



a: b: c a: b: c 2a : b : 2e 



1.092: 1: 0.589 0.551: 1: 1 0.294 1.102: 1: 0.588 



Amphibole (hornblende) 



Amphibole is essentially a metasilicate of calcium and mag- 

 nesium usuallv containing iron and manganese and also sodium 



