PARAGENESIS OF THE ZEOLITES 727 



Mitscherlich observed in 1826 that this change takes place at about 92 degrees, 

 the values given later by Des Cloizeaux, and more recently by Tutton, both 

 of whom used air baths, are from 15 to 2G degrees too high. Nevertheless. 

 Des Cloizeaux's value of 116 degrees Centigrade for red light is the one com- 

 monly quoted. By plotting the values of the apparent angles of the optic 

 axes at various temperatures up to 182.5 degrees Centigrade, it is easily seen 

 that the angle changes most rapidly in the vicinity of the uniaxial point, 

 that is, between 80 and K)0 degrees, and, further, that one axis, as was pointed 

 out by Naumann, changes its position more rapidly than the other. 



PARAGENESIS OF THE ZEOLITES 



BY J. VOLNEY LEWIS 



(AJ)Str(lCt) 



Zeolites and other secondary minerals occur in the Newark igneous rocks 

 of New Jersey. (1) In cavernous spaces in the ropy pahoehoe of the extru- 

 sive Watchung basalts; (2) in fault fissures and fault-breccia of both the 

 basalts and the great intrusive sill (Palisades, Rocky Hill, and Sourland 

 Mountain) ; (3) less commonly in the ordinary joint cracks of both the extru- 

 sive and the intrusive types. The rocks are essentially the same in both 

 chemical and mineral composition, consisting essentially of pyroxene and 

 plagioclase feldspars, with quartz-bearing and olivine-bearing facies. The 

 zeolites and related silicates are essentially combinations of the feldspathic 

 elements and water, with the addition of fluorine in apophyllite and boron in 

 datolite ; the accompanying amphibole, biotite, chlorite, epidote, serpentine, 

 and talc are derivatives of the pyroxenes. Hypotheses of origin dependent 

 on the action of meteoric waters are inapplicable on account of difificulties of 

 circulation, deoxygenation, and sources of fluorine and boron ; on the other 

 hand, contact metamorphism by the intrusives has produced in the adjacent 

 shales minerals into which fluorine and boron enter, presumably by emana- 

 tion from the magma. Hence magmatic waters are regarded as the most 

 probable agent in the formation of the zeolites and accompanying minerals. 



Discussion 



Prof. A. C. Lane : My experience would rank epidote somewhat higher. 

 Can we not conceive meteoric water working down, growing hotter, dissolving 

 silica, and becoming deoxidized by the reducing action of the basaltic glass 

 containing silica chlorides and hydrocarbons suggested by Brun, and thus 

 being in condition to deposit zeolites? 



Prof. F. R. Van Horn : Professor Lewis spoke of apatite as evidence of 

 deep-seated waters being the cause of foundation of zeolites. I would like 

 to ask if he has been able to distinguish apatite of two origins — one by mag- 

 matic differentiation and another which is associated directly with zeolite 

 minerals. 



Dr. Lewis replied : Apatite has been observed as a rock constituent, but 

 not seen in the vein minerals. It is possible to conceive of meteoric waters 

 penetrating the rock, becoming hotter with depth, and becoming charged with 

 the volatile magmatic emanations to such an extent that they would be prac- 

 tically indistinguishable from magmatic waters^ 



