l8o NEW YORK STATE MUSEUM 



It is obvious that the data in hand are quite insufficient to estab- 

 lish the precise formula of the mineral or minerals involved, but 

 they indicate very clearly the general nature and mineralogical 

 associations of the compounds. The data necessary for the precise 

 determination of the silicate formula could be obtained only by 

 analysing carefully separated samples, and the nature of the 

 material is such as to make separation by heavy solutions an 

 exceedingly arduous task. 



In the foregoing recalculations of analyses i and 2, to determine 

 the composition of the ferrous silicate, it was assumed that all the 

 C0 2 present was combined with calcium and magnesium. As a 

 matter of fact, this is doubtless not the case for, almost without 

 question, some CO 2 is combined with iron, thus reducing the amount 

 of iron and increasing the amount of magnesium in the silicate. 



The limit in this direction is obtained by calculating all the CO 2 

 left from calcium carbonate to iron carbonate and including all the 

 magnesium in the silicate. 



The results of such calculation are shown in 16 and 2b as follows: 



Si0 2 



AhOs 



FeO ' 



MgO 



H2O 



While the figures depart considerably from those of ia and 2 a, 

 the replacement of FeO by an equivalent amount of MgO does not, 

 of course, change the essential composition of the mineral as expressed 

 by a formula. The true composition is doubtless somewhere 

 between the extremes represented, respectively, in ia and ib and 

 2a and 26. 



Thus there appears "to be sufficient evidence for classing the ferrous 

 silicate of the gray oolite as chamosite, at least if the name be used 

 in the rather general sense given to it by Lacroix 1 and many others, 

 even if not in the more exact sense assigned to it by Zalinski. 2 



It is evident that the silica in the above analyses is of two sources — 

 clastic and chemical — being, in part, detrital quartz and, in part, 

 precipitated from solution. The same is true for the Clinton ores, 

 in general, but in the ores, as contrasted with the gray oolite, by 

 far the larger part of the silica is of the former origin. 



1 Lacroix, A., Mineralogie de la France I, p. 397, 1893-95. 



2 Zalinski, E., Loc. cit. 



1 b 



2 b 



26.49 



25.09 



23 -93 



24.08 



19.09 



29.11 



17.79 



13-44 



12.70 



8.28 



100.00 



100.00 



