THE NONMETALLIC MINERALS. 205 



H 2 O) [Specimen No. 62417, U.S.N.M.], Carnallite (KC1, MgCl 2 , 6H 2 0) [SpecimenNo. 

 40225,. U.S.N.M.], Boracite (2 (Mg 3 B 8 O 15 ) , MgCl 2 ) [Specimen No. 64742, U.S.N.M.], and 

 Douglasite (2KC1, FeCl 2 , 2H 2 O) . Those of secondary formation, resulting from the 

 decomposition of the primary minerals are, nine in number, namely: Kainite (K 2 SO 4 , 

 MgSO 4 , MgCl 2 6H 2 O); Sylvin (KC1) [Specimen No. 62419, TJ.S.N.M.]; Tachydrite 

 (CaCl 2 , 2MgCl 2 +12H 2 O) [Specimen No. 40230, U.S.N.M.]; Bischofite (MgCl 2 , 6H 2 O) 

 [SpecimenNo. 62428, U.S.N.M.]; Krugite (K 2 SO 4 , MgSO 4 , 4CaS0 4 , 2H 2 O) [Specimen 

 No. 62426, U.S.N.M.]; Reichardtite (MgSO 4 , 7H 2 O); Glauberite (CaSO 4 , Na,SO 4 ) 

 [Specimen No. 40229, U.S.N.M.]; Schonite (K 2 SO 4 , MgSO 4 , 6H 2 O) [Specimen No. 

 62418, U.S.N.M.], and Astrakanite (MgSO 4 , 4H 2 0) [Specimen No. 64738, U.S.N.M.]. 

 Only four of these minerals have any commercial value, namely: Carnallite, Kainite, 

 Kieserite, and rock salt. The yield of boracite, which is found in nests in the Carnallite 

 region of the mine, is too insignificant to be classed among those just mentioned. 



The mine may be divided chemically into four regions: (1) The rock salt, (2) the 

 Kieserite, (3) the Carnallite, (4) the Kainite region. 



The rock salt region has almost the same composition throughout. Its character 

 is crystalline, though in this region well-defined crystals are never met with. In 

 other parts of the mine, especially in the Carnallite region, it is found crystallised in 

 the form of the cube [Specimen No. 40222, U.S.N.M.] and the octahedron, sometimes 

 coloured different shades of red and blue [Specimen No. 64731, U.S.N.M.]. Specimens 

 have also been found of varied structure, laminated, granular, and fibrous [Specimen 

 No. 64733, U.S.N.M.]. 



The deposit lying on the top of the rock constitutes the so-called Kieserite region. 

 The thickness of this deposit is about 56 metres, and its average composition as 



follows: 



Per cent. 



Kieserite 17 



Rock salt 66 



Carnallite 13 



Tachydrite 3 



Anhydrite 2 



100 



In the pure state Kieserite is amorphous and translucent, possessing a specific 

 gravity of 2.517. It contains 87.1 per cent sulphate of magnesia and 12.9 per cent 

 water, corresponding to the formula MgSO 4 , H 2 O. Exposed to the air it becomes 

 opaque from the absorption of moisture, and is converted into Epsom salts; 100 parts 

 of water dissolve 40.9 parts of this mineral at 18 C. The solution, however, takes 

 place very slowly at this temperature. 



This deposit has not been worked to any great extent. Its composition is interest- 

 ing as showing the gradual decrease of the proportion of common salt and the com- 

 mencement of the separation of the more soluble salts. 



Each of the two divisions of the mine just described contains only one mineral of 

 importance. The third division, called the Carnallite region, contains a variety 

 of minerals, and to this deposit Stassfurt owes its world-wide fame. The average 

 thickness of this deposit is about 25 metres, and its composition is as follows: 



Per cent. 



Carnallite 60 



Kieserite 16 



Rock salt 20 



Tachydrite 4 



besides small quantities of magnesium bromide. These minerals are deposited in 

 the order given above, in successive layers, varying in thickness from ^ to 1 metre, 

 the different colours of these minerals giving the deposit a remarkable appearance. 



