118 C. II. Warren — Mineralogical Notes. 



The results of the analyses are as follows: 





I. 



II. 



Average. 



Ratio. 



Calculated for 

 (Fe 4 3 )Pb 3 (Si0 4 ) 



Si0 2 .... 



15-51 



15-48 



15-49 



•258 or 3- JO 



15-40 



PbO .... 



55*50 



55-63 



55-56 



•249 3-00 



57-23 



Fe 9 8 -~ 



27*49 



27-52 



27-51 



•171 2-06 



27-37 



X 



•83 



'8 1 



•82 

 •68 







H 2 .... 



•68 



•67 







100-06 100-00 



The ratio of Si0 2 : PbO : Fe 2 3 corresponds closely to 3 : 3 : 

 2 and gives as the composition of the mineral, Fe 4 Pb 3 Si 3 15 , 

 which may also be written as a basic salt of orthosilicic acid 

 (Fe 4 3 ) Pb 3 (Si0 4 ) ,; the radical (Fe 4 3 ) being sexivalent, and 

 the one which occurs in limonite (Fe 4 3 ) (OH) 8 . 



That the analyses of melanotekite and kentrolite, which have 

 previously been made, have failed to yield formulas correspond- 

 ing to the above, is probably owing to the fact that the material 

 has not been sufficiently pure. A list of these analyses is given 

 below ; the liberty having been taken of changing MnO wher- 

 ever it was found to its equivalent of Mn 2 3 , since it un- 

 doubtedly exists in that condition in kentrolite. 



Melanotekite. Kentrolite. 



Lindstrom. Damour. Flink. Calculated for 



I. II. (Fe 4 03)Pb 3 (Si0 4 )3. (Mn 4 3 )Pb 3 (Si0 4 ) 3 



Si0 2 .. 17-32 17-22 15*95 17'68 15'40 15'45 



PbO . 55-26 58-42 59'79 55'72 57'23 57*43 



Fe 2 3 23-18 22*81 5*58 27*37 



Md 9 0, *76 *63 22*26 21*18 27*12 



X*..._ 3*59 *84 ._. CaO -91 



100-00 100*00 



erived from the foregoing an ah 



PbO : R 2 3 Si0 2 



PbO : R 2 3 



•249 : -171 = 3-10 



3 : 2-06 



•248 : -148 = 3*51 



* 3 : 1*83 



•262 : -145 = 3'30 



3 : 1*70 



•268 : *140 = 2*97 



3 : 1*57 



•250 : -168 = 3'54 



3 : 2-02 



Si0 2 

 Author -258 



Lindstrom I... -288 

 Lindstrom II ._ -286 



Damour *265 



Flink... -294 



The ratio of Si0 2 : PbO : R 2 3 to correspond to the author's 

 formula should be 3:3:2, but in all of the earlier analyses 

 except Damour's, the ratio of the silica is a little too high, 

 probably resulting from a slight admixture of quartz or some 

 other silicate, while the ratios of the lead to' the sesquioxides in 

 Lindstrom's and Flink's analyses are nearly 3 : 2. !No 



*X = CaO, MgO, K 2 0, Xa a O, BaO, CuO, FeO. P 2 5 and CI. 



