Rogers— Dahllite (Podolite) from Tonopah, Nevada. 481 



to interpret. It is usually impossible to decide whether the 

 substances mentioned are essential constituents or impurities. 

 A satisfactory explanation must account for the almost inva- 

 riable presence of the carbonate radical, the usual presence of 

 fluorine and a fairly constant ratio of lOCa to 6P0 4 as well 

 as for variations in the amounts of the constituents. 



An analysis by Mr. Postma of a dark brown egg-shaped 

 nodule with radiated structure collected by Mr. K. M. Wilke 

 in Volhynia, Russia, gave the following results : 



Ca -- 38-81 Fe 2 3 1-93 



P0 4 46-82 A1 2 3 3-93 



C0 3 6-46 Insol 3-22 



F none Organic matter 1*87 



CI tr. 



This is a typical analysis, but it contains an excess of CaC0 3 

 over that required for 3Ca 3 (P0 4 ) 2 ,CaC0 3 . 



The following are analyses of the purer phosphate rocks, etc. : 



Ca P0 4 C0 3 F H 2 Misc. O Total 



Naura 37'72 53-04 2-00 



Hanau 35'27 49*17 2-46 



Maiden Island 34'63 48'43 3'23 



Crawford Mts., Utah __ 36 '41 48'59 2'34 0-40 



Pouzillac 35-52 50'04 5'13 0'88 



Mouillac 37-02 50'27 5-45 1-50 



Amberg 37-28 52'93 3-78 1*90 



Florida 35-62 51-93 2'25 2-46 



Beauval 36-98 51-82 2-26 3-40 T75 99-21 



A few contain an excess of CaC0 3 over that required for the 

 dahllite (podolite) molecule. The excess oxygen given in the 

 next to the last column is necessary to give good summations. 

 As phosphate rocks and nodules are not of definite chemical 

 composition, they perhaps do not deserve recognition as min- 

 erals, but as far as can be ascertained they seem to be mixtures 

 of fluor-apatite, vcelckerite, and dahllite (podolite) as repre- 

 sented by the formula 3Ca 3 (P0 4 ) 2 .Ca(F 2 ,0,C0 3 ). Chlorine is 

 practically absent from these substances. The water is proba- 

 bly not essential, but there is a possibility of the substance 

 3Ca 3 (P0 4 ) 2 . CaC0 3 . x3.fi or 3Ca 3 (P0 4 ) 2 . Ca(F 2 ,0,C0 3 ) . xUfi, 

 which will account for varying amounts of water. 



For convenience of the reader I have given the theoretical 

 percentages of the minerals discussed in the form of metals 

 and acid radicals. 



3-02 



2-89 



1-32 



9999 



2-28 



9-13 



1-20 



99-51 



5-48 



7-16 



1-07 



100-00 



1-05 



S-55 



1-55 



98-89 



7-05 



0-80 







99-42 



4-80 



— 



0-08 



99-12 



— 



3-61 







100-00 



3-03 



5-01 







100-30 



