PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 69 



ite from Woodstown, N. J. The optical properties of the glauconites 

 studied are given in the following table : 



Table I. — Optical properties of glauconite 



2E 



1. St. Francis Co., Mo 



2. Woodstown, N. J 



3. Singleton, Tenn... 



4. Piscataway, Md 



5. Cambrian of Minn.. 



6. Tampico, Mexico 



7. Black Hills, S. Dak." 



8. Patuxent Quad., Md., near 



Croom. 



9. Huntington, Greg 



33" 

 50° 

 33°-37° 

 38° 

 31° 

 35° 

 33° 

 24° 



30°-60° 



" Crystal individuals are very rare and the determinations are only approximate. 



(1) Glauconite from St. Joseph Lead Co. mine, near Bonneterre, St. Francis County, Mo. Upper 

 Cambrian age. 



(2) Glauconite from Woodstown, N. J. Cretaceous age. 



(3) Glauconite from Singleton, Tenn. Ordovician age. 



(4) Glauconite from Piscataway, 2 miles southeast of Fort Washington, Md. Cretaceous age. 



(5) Glauconite from Cambrian, of .Minnesota, locality unknown. 



(6) Glauconite from Cretaceous of the Tampico oil district, Mexico. 



(7) Glauconite from Cambrian of Deadwood, S. Dak. 



(8) Glauconite from near Croom, Patu.xent Quad., Md. 



(9) Glauconite from Huntington, Greg. 



The mineral from Huntington, Oreg., was a mineral specimen sub- 

 mitted to the Geological Survey for identification and the exact 

 nature of its occurrence is not known. It forms large compact 

 masses of an earthy texture. In thin section it resembles massive 

 serpentine, with large poorly defined, smearlike areas of birefract- 

 ing material. No sharply defined crystals were observed and the 

 cleavage is not well developed. The chemical composition, which 

 is represented by analysis 13 (Table II) differs from typical 

 glauconite only in being low in EO bases. The indices of refrac- 

 tion are a=1.59, ;8=1.62±.005, the axial angle is variable, 20°-40°, 

 optical character ( — ). Thus the chemical composition and optical 

 properties are those of glauconite, but the habit and structure are 

 different from those of any previously described glauconite. 



CHEMICAL COMPOSITION 



The number of good analyses of glauconite is not large and many 

 of those published are worthless, because in most of the older analy- 

 ses iron has been determined in only one form of oxidation, because 

 very impure material has frequently been used for analysis, and 

 because methods of purification have frequently been faulty. Glinka ^ 

 gives a number of analyses of Russian glauconites, but the results 

 indicate that some of the material was very impure and some of the 

 analyses show an unusually high content of potash. Sonstadt's 



■^ Glinka, K., Zeitschr. Kryst, Min., vol. 39, 1899, p. 390 (abstract from Russian origi- 

 nal). 



