482 Rogers— Dahllite (Fodolite) from Tonopah, Nevada. 



Ca P0 4 F Cl C0 3 O H 2 



Fluor-apatite 39*62 56*55 3*83 — 



Chlor-apatite 38*39 5481 6 80 



Dahllite (podolite) 38*86 55-35 5*79 



Vcelckerite 40*75 57*77 — — 1-48 



Original dahllite 38*34 52*18 8*18 1*30 



Francolite. 39*07 50*62 3*40 5*32 1*59 



I tested the solubility of some specimens of pyromorphite 

 and found that several gave a distinct effervescence in hot nitric 

 acid. Pyromorphite from the Buffalo claim on Lower Sugar 

 Loaf creek in Marion County, Arkansas collected by Dr. J. C. 

 Branner was analyzed* by Mr. Postma with the following 

 results : 



Molecular ratios 



Pb 66*73 0-322} "7 



Ca 4-02 0-100 j" 



P0 4 23-82 0-250 6*0 



C0 3 1-93 0-032 I 



Cl 2-55 0-035 [ lb 



Insol. _. 0-42 



This pyromorphite, which is the polysphserite variety, occurs 

 as a gray or greenish-gray crust on galena and is clearly an 

 alteration product of the galena. It effervesces slightly in cold 

 nitric acid. With the exception of a slight excess of the 

 carbonate radical the analysis is very closely 10(Pb,Ca) : 6P0 4 : 

 1(C1 2 ,C0 3 ). This analysis is considered proof that the carbonate 

 radical may replace chlorine in pyromorphite, as there is not 

 enough chlorine to form the pyromorphite molecule. On 

 account of the accuracy of the chlorine determination there 

 seems to be no doubt of this explanation. Several analyses of 

 pyromorphite cited in Dana's System of Mineralogy show a 

 deficiency in chlorine which may be explained by the presence 

 of either the carbonate radical or oxygen. 



In conclusion I may say that this paper makes no pretense 

 to a final solution of the difficult problem of the chemical 

 composition of apatite, phosphate rock, etc. Many accurate 

 analyses will be necessary for that task. 



Stanford University, California, 

 February, 1912. 



* A closely agreeing analysis is given in Vol. V (p. 87) of Arkansas Geo- 

 logical Survey Reports. 



