Chap. XIII.] kodurite series : kaolinization. 
275 
under the influence of some waters containing a small amount of these reagents, 
and also in the presence of sulphuric acid, which, as is well known, rapidly 
attacks the feldspars.' 
From the results of the reaction of the water on the rock concerned 
it can be said which of these two agents was contained in the waters. 
With carbon dioxide, orthoclase felspar is decomposed in accordance 
with the following equation : — 
SKaAliSieOie +6H20 + 3Ca2= 3(2H20.Al203.2Si02)+3K2C03+ I2Sia2. 
Orthoclase. Kaolin, 
Th e alumina being insoluble in the presence of carbonates is left behind 
as kaolin, while the silica being soluble, is carried away in solution. 
With regard to water containing sulphuric acid Lindgren says l : — 
' Silica is practically insoluble in solutions containing sulphates and chlcrides, 
hydrogen sulphide and free sulphuric acid. Under these conditions, aluminum 
silicates are dissolved and sulphates or chlorides of aluminum are formed, with 
simultaneous separation of sUica.' 
Since, in the Vizagapatam manganese-ore deposits, a large portion of the 
silica has eWdently been taken into solution and the alumina left behind 
as kaolin, the alteration of the rocks of the kodurite series has been 
considered on the preceding pages as due to the action of waters con- 
taining carbon dioxide in solution. 
Vogt, writing on the same subject says that the view held long 
ago by Forchhammer (1835) and Bischoff (1855), that kaolinization is 
due to the attack of water carrying carbon dioxide, must be the cor- 
rect one for the following reasons : — 
' (1) kaolinization is in many cases a surface process, affected by the weak 
carbonic-acid solutions of surface- waters ; (2) at somewhat greater depths, the 
feldspars of the rocks are ( ften converted by similarly weak carbonic-acid waters 
into kaolin, sericite, etc., as well as calcite.' 
On a later page 3 he mentions the three processes that are due to the 
action of waters containing carbon dioxide, or carbonates of alkalies, 
or alkaline earths, in variable proportions. These three processes are 
kaolinization, sericitization, and carbonatization : — 
' In kaolinization, the waters carry so much carbonic acid that the alkaline 
and earthy carbonates are nearly or wholly removed, together with the dissolved 
silica. In sericitization and carbonatization, on the contrary, there is a deposit 
of potassium silicate or calcium carbonate.' 
1 'Metasomatic Processes in Fissure-Veins,' Trans. Amer. Inst. Min. Eng , XXX 
p. 664, (1900). 
2 'Problems in the Geology of Ore-Deposita,' Trans, Amet. Inst. Min. Eng., XXXI, 
p.l50, (1901). 
3 Ibid., p. 157. 
