1070 A TREATISE ON METAMORPHISM. 



He does not include epidote among the abundant metasomatic minerals of 

 fissure veins, but it is certain that this mineral is important in certain deposits 

 which are essentially the same as fissure veins so far as the circulating' water 

 is concerned. For instance, epidote is very important in connection with the 

 Lake Superior copper. All of these minerals are shown (Chapters VI and 

 VII) to be 'characteristic of alterations in the zone of katamorphism and 

 especially of the belt of cementation. The carbonates are produced by the 

 process of carbonation of the silicates, and the separation of quartz is the 

 correlative process. The hydrous silicates are produced from the anhy- 

 drous silicates by a process of carbonation and hydration For instance, 

 Lindgren" says the muscovite is produced from orthoclase and microcline, 

 and he thus writes the reaction: 



3KAlSi 3 O s + H.,0 + C0 2 =KH 2 A1 3 (Si0 4 ) 3 + K 2 C0 3 + 6Si0 2 



It therefore appears that this reaction is one of hydration and carbona- 

 tion, and at the time the muscovite is formed silica is liberated, to be 

 deposited in the walls or in the veins. 



According to Lindgren the kaolin is mainly formed by the alteration 

 of feldspars, and especially the potassium and sodium feldspars. For potas- 

 sium feldspar Lindgren writes the reaction:'' 



6KAlSi 3 O s + 6H 2 + 3C0 2 =3H 4 Al.,Si 2 9 + 3K 2 C0 3 + 12Si0 2 



Thus this reaction, like that of muscovite, is one of hydration and 

 carbonation, but takes place to a greater extent, the resultant minerals 

 being kaolin and quartz. It is not necessary to write here reactions for 

 the zeolites, chlorites, and other hydrous minerals, for these may be found 

 in Chapter V. An examination will show that the reactions producing 

 them are those of hydration and carbonation of anhydrous silicates with 

 the liberation of silica. 



Lindgren mentions also, as subordinate minerals which form by meta- 

 somatic processes, rutile, anatase, garnet, orthoclase, albite, tourmaline, 

 topaz, scapolite, and apatite. These minerals are those which commonly 

 form in the zone of anamorphism. It has already been seen that in those 

 cases in which it is shown that these minerals have developed at the same 



"Lindgren, Waldemar, Metasomatic processes in fissure veins: Trans. Am. Inst. Min. Eng., vol. 

 30, 1901, p. 608. 



l> Lindgren, cit., p. 614. 



