SYLVIN IT 499 



Per cent. 



Potassium sulfate 28.90 



Magnesium sulfate 19-93 



Calcium sulfate 45- 18 



Water 5 . 99 



The percentage of potash corresponding to the above formula 

 is 15.62. It, therefore, contains a considerable excess of potash 

 over kainit, and on account of its freedom from chlorids is pre- 

 ferred for many purposes. 



425. Krugit. This mineral occurs associated with polyhalit 

 and differs from it only in containing four molecules of calcium 

 sulfate instead of two. Its formula is: K,SO 4 .MgSO 4 .(CaSO 4 ) 4 . 

 H 2 O. As it comes from the mines it is frequently mixed with a 

 little common salt. Its mean percentage composition as it comes 

 from the mines is given in the following numbers : 



Per cent. 



Potassium sulfate 18.60 



Magnesium sulfate 14. 70 



Calcium sulfate 61 .00 



Sodium chlorid i .50 



Water 4.20 



The percentage of potash corresponding to the above formula 

 is 10.05. It is, therefore, less valuable than kainit in so far as its 

 content of potash is concerned. This salt also exists in limited 

 quantities and is not likely to become an important article of 

 commerce. 



426. Sylvin. One of the alteration products of carnallit is a 

 practically pure potassium chlorid, which as it occurs in the Stass- 

 furt mines is known as sylvin. The alteration of the carnallit 

 arises from its solution in water, from which, on subsequent 

 evaporation, the potassium chlorid is deposited alone. This min- 

 eral is found in only limited quantities in the Stassfurt deposits, 

 and it therefore does not have any great commercial importance. 



427. Sylvinit. This mineral has been mined in recent years 

 in considerable quantities. It is, in fact, only common salt car- 

 rying large quantities of potassium chlorid together with certain 

 other accidental impurities. It was probably formed by the dry- 

 ing up of a saline mass in such a way as not to permit the com- 

 plete separation of its mineral constituents. The average com- 



