MINERALS FORMED BY METASOMATISM. 683 



the water solutions are in minute openings, in small quantity, and circulate 

 slowly; therefore, it can not be supposed that any considerable amount of 

 material is contributed from an outside source except by injection. This 

 subject is more fully discussed later. (See pp. 764-766.) The reactions 

 which occur are in the direction of deoxidation, silication, and dehydra- 

 tion, instead of in the direction of oxidation, carbonation, and hydration. 

 The minerals formed comprise practically all of the important heavy 

 anhydrous minerals. 



MINERALS FORMED. 



Among the minerals formed in the zone of anamorphism are the 

 following : 



The carbon minerals are anthracite, graphite, or diamond. 



The abundant sulphides are pyrite and pyrrhotite. Marcasite, having 

 lower symmetry and lower specific gravity than pyrite, is rare or altogether 

 absent, although abundant in the belt of cementation. 



The important oxides are those of silicon, iron, aluminum, and titanium. 

 Silica is found in the form of chert, chalcedony, or quartz. Tridymite is not 

 known. Tridymite alters to quartz because of the higher specific gravity of 

 the latter mineral. Iron oxide occurs in hematite, magnetite, and ilmenite. 

 Aluminum oxide occurs as corundum. Titanium oxide is found as rutile, 

 octahedrite, and brookite. The two latter are rare as compared with rutile. 

 This is probably explained by the fact that the latter mineral occupies less 

 volume. The absence of the hydrous oxides, such as limonite, gibbsite, 

 brucite, etc., is explained by the general fact of dehydration characteristic 

 of the zone of anamorphism. 



The carbonates, aragonite, magnesite, dolomite, siderite, ankerite, and 

 parankerite are extensively recrystallized; but the processes as a whole 

 tend to destroy them, forming silicates. Ordinarily, where the carbonates 

 were in large volumes, the process of silication and decarbonation is 

 incomplete. 



The most important sulphate is anhydrite. Gypsum does not occur, 

 because the process of dehydration destroys it. Titanate as titanite, and 

 phosphate as apatite, occur. 



Practically all the important anhydrous silicates are abundant. These 

 comprise the feldspars, the pyroxenes, the amphiboles, the nephelite- 

 sodalite-leucite group, the garnets, the olivines, the scapolites, the epidotes, 



