ART. 16 ZEOLITES FROM OREGON HEWETT, SHANNON", GONYER 5 



there are separate vesicles filled with calcite, with chabazite, and 

 with mesolite. Others show analcite on chabazite, and still others, 

 stilbite on chabazite. Near by, at locality 7, there are vesicles filled 

 respectively with calcite and chabazite as well as others showing the 

 following succession : Calcite, chabazite, pseudomesolite, and stilbite. 

 At locality 1 some of the vesicles near the top of the lowest flow are 

 filled with calcite, others with chabazite, and still others with meso- 

 lite. At locality 2 some of the vesicles at the top of the middle flow 

 are filled with chabazite; others show crusts of mesolite on calcite. 

 Paragenesis — In many places near the spring, as noted above, 

 certain zeolites occur in abundance but not associated with other 

 zeolites. There are summarized below the order of deposition of the 

 zeolites and other minerals where two or more are associated and 

 their relations are clear, the numbers indicating the localities shown 

 on the map. 



1. Chabazite, mesolite (or pseudomesolite). 



2. Calcite, mesolite. 



6a. Chabazite, analcite. 



6&. Chabazite, stilbite. 



1. Calcite, chabazite, pseudomesolite, stilbite. 



8. Mesolite, calcite, opal. 



9a. Calcite, chabazite, pseudomesolite. 



9&. Mesolite, pseudomesolite. 



10 (fissure). Calcite, stilbite, calcite. 



12. Mesolite, analcite. 



From this summary it is clear that there is not a simple order 

 of deposition for the entire area in which each mineral appears 

 but once. On the other hand, if the minerals of the fissure be 

 ignored the simplest succession indicated is as follows: 



1. Calcite (CaCO,). 



2. Chabazite (CaO.Al^-^ SiO,>.6H.,0). 



3. Mesolite ([CaO, Na^OJ.AlA-S SiOo.SH.O). 



4. Pseudomesolite ([CaO,NaoO].Alo03.3 SiO,.3 H,0). 



5. Analcite (Na20.Alo03.4 SiOo.2H,0). 



6. Stilbite (CaO-ALoVeSiCGHoO"). 



7. Opal (SiO^ + H.O). 



This sequence does not take into account thomsonite which, though 

 abundant in one locality, is not associated with another zeolite. It 

 would seem that in the area outside of the fissure there was a tend- 

 ency for the least siliceous minerals to be deposited first and the 

 most siliceous last. Unfortunately, the fissure contains but two 

 minerals, one of which, calcite, is repeated, and the sequence does 

 not confirm the conclusion stated above. 



Genesis. — The association of the zeolite-bearing areas, the fault 

 fissure and the active hot spring indicate a genetic relation between 

 them. The age of the fault is obscure, but it was probably formed 



