46 ON THE POSITION OF LIBVRITE IN THE MINERAL SERIES. 



to this idea ; but it. appeared at least possible that the crystallized 

 specimens might be able to take up a certain proportion, and no more, 

 of the magnetic oxide. I calculated therefore from the four first 

 analyses given above, the mean composition of Lievrite, and reduced 

 this, with the following results, to 100 parts : — 



Silica 29.54 = 29.66 



Sesquioxide of Iron 23.08 = 23.25 



Protoxide of Iron 31.25 = 31.49 



Protoxide of Manganese 1.35 = 1 . 46 



Lime 14.04 = 14.14 



99.26 100.00 



Now, 23.25 parts of Fe^O^ require 10.46parts of FeO to form magne- 

 tic iron ore (= FeO, Fe^O^). This deducted from 31.49, leaves 21 .03 

 for the protoxide of iron present (on the above supposition) in the 

 silicate. The analysis consequently stands as below : — 



Silica 29.66 =x 44.75 



Protoxide of Iron 21.03 = 31.72 



Protoxide of Manganese 1.46 = 2.20 



Lime 14.14 = 21.33 



66.29 100.00 



Calculating the oxygen ratios of the above, we obtain : — 



Si02 23.24 = If = 7 = 14 



FeO 1 



MnO > 13.59 = 1 = 4 = 8 



CaO J 



Here, then, we have 8 atoms of RO to 7 atoms of SiO^, in place of 

 2 to 1 as required by the chrysolite formula. If the oxygen ratios in 

 any of the above analyses had come out as 9 : 6 : 14, we might have 

 written the formula 7 (RO, SiO^) + 2 (FeO, Fe^O^,); but the 

 analyses do not yield these values. The view, therefore, as suggested 

 above, that the peculiar composition of Lievrite may arise from the 

 presence of magnetic iron ore, cannot be sustained. 



But the formula of Lievrite may be brought to coincide with that 

 of the Chrysolite series, by assuming the iron to have been originally 

 present in the condition of FeO only. If this be assumed — and the 

 assumption is in part warranted by the well-known fact that Lievrite 

 is especially subject to alteration, the conversion of the FeO into Fe» 

 0£, still going on in many specimens — the difficulty is at once removed. 



