﻿310 Penfield and iSperry — P seudomorphs of Garnet. 



the ratios are sufficiently close to justify us in referring the 

 material to that species. 



It should be stated that all these analyses were made in 

 duplicate from carefully selected air-dried material, none of 

 which lost more than O10 per cent at 100° C. Fe o 3 was 

 determined in every case when present. Although these analy- 

 ses do not indicate well-defined species, they show clearly what 

 changes the garnet has undergone. The microscopical exami- 

 nation did not reveal anything not noticed by Mr. Pumpelly in 

 his article already referred to. 



2. Decomposed garnets from Colorado. 



We have also examined the pseudomorph garnets from 

 Salida, Chaffee Co., Colorado. The garnets were large dode- 

 cahedrons coated with chlorite. They differ from the Lake 

 Superior garnets in that the decomposition forms only a coating, 

 while the interior of the garnet crystal is quite homogeneous. 

 One large crystal, 7 cm in diameter, is in the collection of Pro- 

 fessor Geo. J. Brush. We are indebted to Mr. Whitman 

 Cross of the U. S. Geological Survey for information concern- 

 ing the correct locality in which these specimens occur, and 

 to Mr. L. Gr. Eakins for the material which he kindly pro- 

 cured for us from a mineral dealer in Colorado. The mate- 

 rial was obtained by scraping off the thin coating of chlorite, 

 which was readily removed from the hard garnet. The analyses 

 of this material are given below. 



Garnet. Decomposition product 











alter deducting 1*84 per cent 



Specific gravity 4-163 





of garnet. 



Si0 2 = 



37-61 



per 



cent. 



28-20 per cent. 



A1„0 3 = 



22-70 







22-31 



Fe;0 3 















FeO = 



33-83 







19-11 



MnO = 



1-12 











Mo-0 = 



3-61 







17-68 



CaO = 



1-44 







•48 



Xa 2 











•72 



K 2 











1-03 



H 2 











10-90 



100-31 100-43 



From the above analyses, it will be seen what changes have 

 taken place here. It is essentially the same change that the 

 Lake Superior garnet has undergone, with the exception that a 

 greater quantity of magnesium has replaced the protoxide of 

 iron. The ratios of the above analyses are : 



