P0 4 



F 



C0 3 



CI 



54-03 



3-38 



1-17 



0-09 



55-40 



1-95 



1-93 



0-94 



55-52 



1-17 



3-14 



0-42 



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



The isomorphism, or at least the replacement of fluorine by 

 the carbonate radical, is proved by several analyses* of apatite 

 taken from the literature. 



Ca 



Portland, Canada 38*62 



Londongrove, Penn 3 8 -5 3 



Terapleton, Canada 37*77 



The second analysis, made by Carnot,f corresponds almost 

 exactly to the formula 3Ca 3 (P0 4 ) 2 .Ca(F 2 ,Cl 2 ,CO s ). 



I have examined apatite from fourteen different localities 

 and have found that, with one possible exception, they give 

 effervescence in hot nitric acid. These include apatites from 

 Canada, Arkansas, ^Norway, among them both fluor-apatites 

 and chlor-apatites. It may seem strange that fluorine and the 

 carbonate radical should replace each other and that the com- 

 pounds 3Ca 3 (P0 4 ) 2 .CaF 2 and 3Ca 3 (P0 4 ) 2 .CaC0 3 should be 

 isomorphous. The isomorphism of these compounds can be 

 explained by the mass-effect of 3Ca 3 (P0 4 ) 2 .Ca (formula weight 

 =971) in these compounds ; the fluorine and carbonate radical 

 have relatively little influence. This explanation of isomor- 

 phism we owe to Penfield, who explained the chemical com- 

 position of tourmaline by the mass-effect of Al 3 (B.OH) 2 Si 4 19 

 in the molecule H 9 Al 3 (B.OH) 2 Si 4 19 , it making little difference 

 whether the hydrogen is replaced by aluminium, magnesium, 

 iron, or the alkalies. The isomorphism of PbFe 6 (OH) 12 (S0 4 ) 4 

 (plumbojarosite) with K 2 Fe 6 (OH) 12 (S0 4 ) 4 (jarosite) Penfield 

 explained in the same way. A similar explanation will doubt- 

 less hold for other mineral groups. 



A critical study of apatite analyses will convince one of the 

 existence of a basic calcium phosphate, for many of the 

 analyses show a deficiency of both fluorine and chlorine and 

 also of the carbonate radical. In tabular form I have collected 

 here several apatite analyses showing this deficiency. The 

 oxygen is obtained by subtracting the sum of the constituents 

 in the present form from their sum as oxides. The almost 

 perf ect summations prove that this is justified. It was thought 

 that perhaps the carbonate radical had been overlooked in 

 these apatites. Accordingly Mr. Postma analyzed a specimen 

 of Zillerthal apatite, obtained from Dr. Krantz of Bonn, Ger- 

 many. This apatite occurs in large white tabular crystals. 

 Mr. Postma's analysis, which is the last one in the preceding 

 list, shows only a slight amount of the carbonate radical. 



* These and other analyses have been recalculated in the form of metals 

 and acid radicals. 



f Bull. Fr. Soc. Min., xix, 135, 1896. 



