ALTERATIONS OF MEIONITE AND MARIALITE. 313 



Supposing all of the CaC0 3 to remain as calcite, the increase of volume is 

 35.40 per cent. 



The passage of the scapolites into muscovite may be written as follows: 



For marialite: 



(3) 2Na 1 Al3Si 9 M Cl+K 2 C0 3 +2H 2 0+2CO,=2KH 2 Al 3 Si 3 12 +12Si0 2 +2NaCl+3Na 2 cb 3 +k. 



In this reaction, as in the case of the passage of the acid feldspars into 

 muscovite, a large amount of the silica separates. The decrease in volume 

 of the muscovite and quartz as compared with the marialite is 16.74 per 

 cent, but if the soluble sodium salts be also taken into account the volume 

 is increased. 



For meionite the reaction may be — 



(4) Ca 4 Al 6 Si 6 25 +K 2 C0 3 +3C0 2 -2H 2 0=2KH 2 Al 3 SiA 2 +4CaC0 3 +k. 



The increase in volume of the muscovite and calcite as compared with the 

 meionite is 29.42 per cent. 



As the composition of epidote is very analogous to meionite, and as it 

 is a calcium-bearing compound, it is thought likely, where epidote is second- 

 ary to a scapolite, that it is derived from a meionite molecule. Therefore, 

 supposing that the epidote is one in which the aluminum is to the iron as 

 2:1, and supposing that the iron is derived from ferric oxide (Fe 3 3 ), the 

 reaction may be written as follows: 



(5) Ca 1 Al 6 Si 6 25 +Fe 2 3 +4H,0=2HCa 2 Al 2 FeSi 3 ]3 4-2Al(OH) 3 +k. 



Supposing the hematite (hexagonal-rhombohedral; sp. gr. 5.225) to have 

 been present as a solid, and the gibbsite to remain as a solid, the decrease 

 in volume is 1.62 per cent. It is thought likely that iron for the reaction 

 is often derived from iron carbonate in solution, combined with simulta- 

 neous oxidation. In this case the reaction would be — 



(6) Ca 4 Al 6 Si 6 25 +2FeC0 3 +4H 2 0+0=2HCa,Al 2 FeSi 3 13 +2Al(OH) 3 -f2C0 2 +k. 



The increase in volume of the epidote and gibbsite as compared with the 

 meionite is 7.55 }Der cent. 



The passage of marialite into kaolinite and talc involves hydration, 

 expansion of volume, and liberation .of heat. The change of meionite to 

 kaolinite involves hydration, carbonatien, increase in volume, and libera- 

 tion of heat. The change of the scapolites to muscovite and accompany- 

 ing compounds are reactions of hydration, carbonation, increase of volume, 



