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ANNALS NEW YORK ACADEMY OF SCIENCES 



dent than is the case with the smaller form of albite crystals, but it is 

 believed that the same process prevailed in a slightly modified form. 

 Crystals of the larger type are best seen in slides 133 and 134. The hand 



Fig. 4. Single crystal of secondary albite showing both carlsbad and albite 

 twinning. Crossed nicols. X 35. Slide 13.3. 



specimen from which both of these slides were prepared shows numerous 

 clear, glassy crystals imbedded in pectolite. The microscopic appearance 



Fig. 5. Crystal of secondary albite partly replaced by pectolite. Outline is 

 corroded and interior clouded in places, and pectolite fibres are advancing 

 across it. X 35. Slide 134. 



of a single crystal between crossed nicols is shown in fig. 4, and one in 

 which the albite has been partly replaced by pectolite is shown in fig. 5. 



