FENNER, THE WATCHUNG BASALT 



135 



In 138, a large apophyllite crystal carries a great variety of inclusions, 

 most of which are in process of replacement by the apophyllite. They 

 comprise quartz, garnet, amphibole, prehnite, pectolite and calcite. 

 Fragments of quartz are numerous. Eelations to both apophyllite and 

 prehnite are shown in fig. 9. The prehnite carries a sharply defined im- 

 pression of a quartz pyramid, but only portions of the quartz crystal are 

 left. The remainder of the space is occupied by apophyllite. The rela- 

 tions indicate that prehnite was deposited upon the terminal pyramid of 

 a quartz crystal and that later both were removed during the formation 

 of apophyllite or were partly incorporated within the latter. 



In 87, fragments of quartz are inclosed in prehnite and pectolite in 

 such a manner as to indicate replacement by both. In fig. 10, the rela- 



FiG. 11. Replacement of quartz (clear) by chabazite (blocky). The quartz 

 extinguishes nearly as a unit. Outside the field the radiating crystals of 

 quartz spring from a centre. X 35. Slide 77. 



tions of quartz and chabazite in slide 146 are illustrated. The contact 

 along one margin is perfectly straight, and it appears that corrosion has 

 had no effect there. In other places, the quartz is greatly attacked, and 

 chabazite has replaced it. A narrow vein of chabazite crosses the crystal, 

 probably following some minute crevice which gave access to the solu- 

 tions, and in various places lines of turbidity show the manner in which 

 replacement begins. 



In 77, replacement of quartz by chabazite in somewhat different rela- 

 tions appears. Heulandite also replaces the quartz. It is believed that 

 the slide as a whole illustrates a frequent form of attack and replacement 

 of quartz by later minerals. Figs. 11 and 12 show characteristic features. 

 The original habit of the quartz in this slide seems to have been as groups 



