53 
GENESIS. 
The proved chemical properties of the mineral form a basis 
upon which to build up the steps by which the mineral has been 
formed, though no theory of origin can be considered final until the 
deposit in which the mineral occurs has been traced below the zone 
of oxidation. 
Tlie genesis of alunite, the commonest mineral of this group, 
is usually ascribed to solfataric action on rocks containing large 
quantities of orthoclase. Thus: 
6KAlSi 3 O s + 6S0 2 -f 30 2 + 6H 2 0 = 
Orthoclase. 
6H 2 0.K 2 0.3A1 2 0 3 .4S0 3 + 2K 2 S0 4 + LSSiO, 
Alunite. 
In the customary presence of other aluminous silicates, such as 
oligoclase, etc., no free potassium sulphate would be produced, the 
whole of it combining with aluminium sulphate to form alunite. It 
is. to be noted that a mixture of sulphur dioxide and oxygen are 
necessary to produce this effect. Such a .mixture has indeed been 
recorded in gases from two volcanoes, Hekla and Vulcano*, but 
must be far from common in sub-surface fissures. 
On the other hand alunite might well be produced by the 
weathering of an “alum slate” containing much serieite and pyrites 
or marcasite, thus : 
2H 2 0'.K 2 0 . 3 A1 2 0 3 .6 Si0 2 + 2FeS 2 -f 7H 2 0 + 150 = 
Serieite. 
GH 2 0.K 2 0.3A1 2 0 3 .4S0 3 -f Fe 2 (HO) 6 + GSi0 2 
Alunite. 
The Kundip Natrojarosite is almost certainly not the result of 
solfataric action, but the product of the weathering underground of 
pyritous ore in the presence of sodium-bearing rocks and ground 
waters. 
The normal equation for the first stage in the weathering of 
pyrites f in a quartz reef or elsewhere, where easily decomposed 
rock silicates and carbonates do not come into action, is 
2FeS, + 2H 2 0 -f 70 2 = 2FeS0 4 + 2H 2 S0 4 . 
With additional penetration of atmospheric oxygen, further oxida- 
tion of the ferrous sulphate takes place, thus : 
2Fe'S0 4 + 2H 2 S0 4 + 0 = Fe 2 (S0 4 ) 3 + H 2 S0 4 + H 2 0. 
It is seen that the oxidation of ferrous sulphate to ferric sulphate 
reduces the acidity of the solution to one-half, thus increasing the 
tendency to formation of basic salts. 
* F. W. Clarke, Data of Geochemistry, Edit. II., pp. 249-251. 
1 Van Hise. Treatise on Metamorp iism, p. 214, does not give this equation. 
He gives, h >wever, five others as representing prob hie reactions, during the sub- 
surface weathering of pyrites. One of these gives H 2 S and S0. 2 , two incompatibles, 
as simultaneous products of the reaction ; a second gives f -rric hydrate with a con- 
siderable excess of SO.,; a third, ferric hydrate with abundant sulphuric acid! 
These equations appear to require some explanation.— E.SS. 
