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PKOCEEDINGS OF THE ZsTATIOFAL MUSEUM. 



VOL. 64 



essentially pure and homogeneous by optical study. The percentages 

 and ratios obtained are as follows: 



Analysis and ratios of heulandite. 



This analysis gives the formula (Ca,K2,Na2)O.Al203.7Si02.5H20. 

 This differs from the formula for heulandite given by Dana in con- 

 taining one more molecule of silica. The replacement of lime by 

 alkalies has, furthermore, progressed to the point where the com- 

 bined soda and potash are in excess, both molecularly and by 

 weight, of the lime. 



A form of heulandite of somewhat different properties occurs 

 rarely in the amygdaloid rock as small solid pebblelike bodies coated 

 on the outside by deep green chlorite and, where fractured, showing 

 coarse granular structure, well defined cleavage, pearly luster, and a 

 faintly pink color. A similar material occurs as drusy crusts of 

 brilliant crystals of faintly pink color lining small flat open cavities 

 in the rock adjacent to the large masses of mordenite. These 

 crystals when examined optically are seen, like the preceding, to be 

 made up of sectors not identical in extinction angle, the angle between 

 adjacent sectors varying 10° or more. Moreover, they are strongly 

 zoned, the outer zone having the following optical properties: Biaxial^ 

 positive ( + ), 2V = 68°, a= 1.494, i3= 1.496, 7=1-501, 7-«=0.006, 

 while the properties of the cores are: Biaxial positive ( + ), 2V = 90°, 

 a =1.483, ^=1.487, 7=1.490, 7-"= 0.007. Crystallographically 

 these are, like the others, in fair agreement with the heulandite angles,, 

 the forms identified being 6(010), m(llO), c(OOl), ^(101), s(TOl), 

 2(011), and w(032). The latter is a rare form previously noted only 

 on heulandite from Scotland. In habit these pale crystals are much 

 stouter than the others, as shown in figures 3 and 4, and they are 

 grown together in parallel groups over considerable areas, the plane 

 of contact being &(010). 



ANALCITE. 



Analcite occurs as single crystals and groups of aggregated crystals 

 embedded near the centers of the larger masses of cottony mordenite 

 and as crusts and druses of crystals lining cracks in the adjacent 



