ALMANDITE AND ITS SIGNIFICANCE 



659 



Limestone X — = Garnet Rock Difference 



I 



SiOa. 266 =63574 880 —62694 



AI2O3 I 239 239 O 



FeA 1 18 



FeO / 9 21S1 ,56 -1977 



CaO 832 198848 21 -198827 



MgO 137 32743 60 -32683 



NazO o o 47 47 



K2O o o 16 16 



The change from limestone to garnet rock involves a loss of 



everything but alkalies. Much of the lime and magnesia has been 

 removed in solution and carried into the upper zones which are now 



Fig. 3. — Garnet in limestone. (Magnification about 30 diameters. Ordinary 

 light.) The photograph shows garnet (high relief) in the center of the field; it is 

 surrounded by a broad kelyphite rim, which seems to be an incipient stage in its 

 formation. The remainder of the field is largely carbonates. 



eroded away. The apparent loss of iron and silica is due to replace- 

 ment of the lime and magnesia by these constituents. From 

 chemical analyses alone it is difficult to follow the changes, since 

 an addition in one rock has the same effect as the loss of the same 



