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PEOCEEDINGS OF THE NATIONAL MUSEUM. 



Crystals of similar form, size, and color but etched and dull were 

 found in April, 1923, in a north-south vein near the north end of the 

 quarry face, associated with datolite, prehnite, and laumontite, and 

 definitely later than all of these. 



Crystals of similar habit but smaller and of a greenish color were 

 seen overlying chabazite druses on horizontal cracks in diabase near 

 the southwest corner of the quarry. 



The stilbite crystals showing pyramid planes which form broad 

 limonite stained druses on basalt are often overlain by calcite crystals 

 which are either scalenohedral or rhombohedral in habit. Some of 

 these are minute but others, of flattened rhombohedral form, reach 

 1 cm. in greatest dimension and some obscure flattened crystals of 

 hexagonal outline are 3 cm. across. 



One translucent white calcite crystal 3 mm. long, which rested upon 

 prehnite, had the habit shown in figure 32 and gave the following 

 angles : 



Angles of calcite crystal, Figure 32. 



Calcite occurs also as indistinct radial fibrous globular masses over- 

 lying a small botryoidal crust of opal on a specimen of ordinary 

 basalt. The globular patches of calcite reach a diameter of 5 mm. 



Galena is a rare constituent of the zeolite-bearing vein fillings but 

 was noted several times, as small isolated crystals with perfect cubic 

 cleavage. It was found embedded in chlorite, in prehnite, one of 

 the earlier minerals, and in apophyllite, one of the latest minerals 

 of the veins. 



CHALCOPYRITE. 



Chalcopyrite is also rare in the later veins, being comparable with 

 galena in this respect. Like galena it was noted in isolated crystals 

 inclosed in prehnite and in apophyllite. It is much more common 



