SILICA-CARBONATE ROCK 



63 



lions to show chemical changes involved in the formation of 

 silica-carbonate rock from serpentine 



1. Average of 3 serpentines : 1 and 2 of table 1 1 and 1 of table 12. 



2. Average of3silica-carbonaterocks:4and5of table 11 andSof table 12. 



3. Column IX Avgspgr of 2. 46. 



4. Column 2X Avgspgr of 2.82. 



5. Column 4 minus 3. 



FIGURE 47. Diagram showing gains and losses by weight of principal 

 oxides in hydrothermal alteration of a unit volume of serpentine to 

 silica-carbonate rock, assuming volume for volume replacement. 



amount of migration of the constituents is indicated 

 by the arrangement of the replacing minerals. Never- 

 theless, the preservation of the larger textures and 

 structures indicates there has been no appreciable 

 change in volume, and a consideration of chemical 

 analyses along with specific gravities shows that in 

 spite of limited migrations the change is principally 

 one of simple dehydration and carbonatization. The 

 chemical changes are shown in table 13 and also in 

 figure 47. Columns 1 and 2 of the table present the 

 averages of three analyses of serpentine and of silica- 

 carbonate rocks derived from nearby parts of the same 

 serpentine bodies. As the specific gravity of serpen- 

 tine and silica-carbonate rock is different, columns 3 



