REDISTRIBUTION OF POTASSIUM. 1001 



illustrated at Stassfurt, where, as already noted (p. 994), from 1876 to 1880 

 the amount of carnallite (KMgCl 3 .6H 2 0), kieserite (MgS0 4 +H 2 0), and 

 kainite (MgS0 4 .KCl+3H 2 0) mined was 699,136 metric tons, whereas the 

 amount of rock salt was for the same years only 96,856 metric tons. Since 

 the salt deposits are so important, it follows that the total amount of 

 potassium in such deposits is large. 



It seems probable that the potassium in the salts of inland seas and in 

 the saline deposits is sufficient to account largely and perhaps fully for the 

 remaining two-thirds of the deficiency of potassium in the sediments. 



Where the rocks which contain potassium are altered in the zone of 

 katamorphism, the potassium-bearing minerals . do not decompose to the 

 same extent as the sodium-bearing minerals. So far as the potassium is in 

 leu cite, it readily alters ; but, as already noted, the greater part of the potas- 

 sium is in orthoclase and microcline, and these are the most difficultly 

 decomposable of the feldspars. These minerals disintegrated and only par- 

 tially decomposed are carried in great quantities to the sea. But even 

 where the potassium feldspars are decomposed, it seems that the potassium 

 is held in an insoluble form to a large extent. Prestwich" attributes the 

 retained potassium to the action of alumina, although he does not explain 

 the reaction by which it is held. Mendeleeff'' emphasizes the absorptive 

 power of the soil, and especially of the vegetable mold, for potassium. It 

 is known that potassium compounds are used by plants to a much greater 

 extent than sodium compounds. But the influence of plants in retaining 

 potassium can not be cited to explain the apparent concentration of 

 potassium in the muds. It ajDpears to me that where the feldspars have 

 decomposed and the potassium largely remains in the silts and muds, it is 

 likely that this element has passed into the zeolites, especially apophyllite. 



When the rocks formed in the zone of katamorphism are buried in the 

 zone of anamorphism, the original minerals which contain the potassium 

 may be produced, but it has already been seen that the chief minerals 

 originally holding the potassium are orthoclase and microcline. It has 

 further been pointed out that the soda minerals are much more readilv 

 decomposed and that much less of the sodium is left in the sedimentary 



a Prest\vich, Joseph, Geology — chemical, physical, and stratigraphical, vol. 1, 1886, p. 54. 

 6 Mendeleeff , D., The principles of chemistry, translated by Geo. Kamensky, Longmans, Green 

 & Co., London, vol. 1, 1897, pp. 546-547. 



