.ABT. 2. 



PETROLOGY AT GOOSE CREEK SHANNON. 



67 



A small vein in the south end of the quarry varied from 1 to 2 cm. 

 wide and was filled with granular fine green porous prehnite. The 

 cavities are lined with brilliant little crystals which are elongated on 

 the a axis and have the crystal habit shown in the orthographic and 

 clinographic drawings of figure 12. The prism faces gave good 

 measurements indicating the prismatic angle to be 80° 59'. The 

 front pinacoid also gave good signals but 

 the side pinacoid (010) is etched dull. The 

 base is horizontally striated as indicated. 

 Between crossed nicols these crystals gave 

 the pattern shown in figure 19. Although 

 at first glance appearing more complicated, 

 this is found to be only a variation of the 

 structure shown in figure 18, and is capable 

 of the same interpretation. 



These interpretations are applicable only 

 to the prehnites here described and this 

 mineral seems to adopt numerous other con- 

 fused intergrowths producing other effects 

 as shown by the discussions of Mallard and 

 Emerson abstracted in Dana's Mineralogy. 



The green prehnite from one of the sheeted 

 veins was purified for analysis and analyzed 

 in the Museum laboratory yielding the results 

 given in column 1 below. In column 2 are 

 quoted the results obtained on analysis of 

 prehnite from Admiralty Inlet, and in column 

 3 the theoretical composition. 



Fig. 21. — Datolite of second 

 generation showing moee 

 prismatic habit by elonga- 

 TION ON THE a AXIS 



Analyses of prehnite. 



