1873. J 40d [Qenth 



101.65 100.06 100.27 100.14 100.45 



It will be observed that in some of the margarites a cousiderable quan- 

 tity of alcalies (R 2 0), especially soda, replaces lime. This is especially 

 the case with «1, iu which one-third, and e and hi and 2, in which about 

 one-sixth of the lime is thus replaced. 



Although many of these analyses were made only for the purpose of 

 determining the species — in general they agree well with the established 

 oxygen ratio for RO : R,0 :J : SiO, : H,0 = 1 : 6 : 4 : 1. 



Some contain a larger quantity of water. 



I must not omit to notice here the description of a very important 

 specimen which J. L. Smith (I. c.) gives in his memoir on emery : A 

 nodule, containing emery in the centre, icith two concentric layers, the inner 

 of chloritoid, the outer of emerylite (margarite;. In other words a pseudo- 

 morph of chloritoid and margarite after corundum ! 



28. Earthy aIjxeral from Gainesville, Georgia. 

 Associated with and forming the matrix of some of the Gainesville 

 margarite and resulting, like the latter, from the alteration of corundum 

 is an earthy mineral, of which I have made an analysis. Its structure is 

 finely granular ; it is soft, but contains some hard particles which appear 

 to be quartz. Its color is between isabel-yellow and riesh-color. Very 

 minute particles of margarite are intermixed with it. 



Sp. Gr. = 2.851. 

 Quartz = 2.17 



Si0 2 = 28.84 contains oxygen 15.38 



Al,6, == 39.65 18.48 \ 



Fe,0 3 = 2.12 0.64 J 



MgO = 1.20 0.50 1 



CaO = 14.75 4.21 



N&,0 = 0.48 0.12 f 



K 2 = 1.60 0.27 j 



Ignition == 10.41 9.25 



101.28 



19.12 



5.10 



