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, would be preferred for many purposes.

240. 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: K₂SO₄·MgSO₄·(CaSO₄)₄·H₂O. 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:

Potassium sulfate18.60 per cent.
Magnesium sulfate  14.70““
Calcium sulfate61.00““
Sodium chlorid1.50““
Water4.20““

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.

241. Sylvin.—One of the alteration products of carnallit is a practically pure potassium chlorid which, as it occurs in the Stassfurt 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 mineral is found in only limited quantities in the Stassfurt deposits and it therefore does not have any great commercial importance.

242. Sylvinit.—This mineral has been mined in recent years in considerable quantities. It is, in fact, only common salt carrying large quantities of potassium chlorid together with certain other accidental impurities. It was probably formed by the drying up of a saline mass in such a way as not to permit the complete separation of its mineral constituents. The average composition of sylvinit as it comes from the mines is given in the following table:

Potassium chlorid30.55 per cent.
Sodium chlorid46.05“
Potassium sulfate6.95“
Magnesium sulfate4.80“
Magnesium chlorid2.54“
Calcium sulfate1.80“
Water and insoluble  7.29“

This salt is richer in chlorin than any other of the Stassfurt potash minerals, containing altogether 79.14 per cent of chlorids. Its potash content amounts to 23.04 per cent, but in proportion to the potash which it contains, it is relatively poorer in chlorin than kainit and carnallit. On account of its high content of potash the freights on a given weight thereof as contained in sylvanit are lower than for kainit and carnallit.

243. Kieserit.—The mineral kieserit is essentially magnesium sulfate and it does not necessarily contain any potash salts. Under the name of kieserit, however, or bergkieserit, there is mined a mixture of carnallit and kieserit, which is a commercial source of potash. The mixture contains the following average content of the bodies named:

Potassium chlorid11.80 per cent.
Magnesium sulfate21.50“
Magnesium chlorid  17.20“
Sodium chlorid26.70“
Calcium sulfate0.80“
Water20.70“
Insoluble1.30“