The carnallite principally dissolves and crystallizes out relatively pure on cooling.
There is also deposited a double magnesium and potassium chloride, similar to the carnallite of Stassfurt, and finally the mother-liquor, which has now again risen to specific gravity 1.3374, contains only pure magnesium chloride.
The salt is commonly associated with gypsum, often also with anhydrite, and occasionally with sylvite, carnallite and other minerals containing potassium and magnesium.
The Stassfurt deposits are of special importance for the sake of the associated salts of potassium and magnesium, such as carnallite and kainite.
In thickness of carnallite, MgC1 2 KC1.6H 2 O, mixed with a little salt; this is followed by a thicker deposit of kieserite, MgSO 4 H 2 O, containing rather more salt than the upper bed.
It is found in the minerals lepidolite, petalite and in various specimens of mica and of carnallite, and in some mineral waters.
Chlorine is never found in nature in the uncombined condition, but in combination with the alkali metals it occurs widely distributed in the form of rock-salt (sodium chloride); as sylvine and carnallite, at Stassfiirt; and to a smaller extent in various other minerals such as matlockite and horn-mercury.
Very thin laminae of haematite, blood-red by transmitted light, occur as microscopic enclosures in certain minerals, such as carnallite and sun-stone, to which they impart colour and lustre.
News, 1864, 10, p. 181), and, associated with rubidium, at Diirkheim; it is also found in lepidolite, leucite, petalite, triphylline and in the carnallite from Stassfurt.
These deposits, in addition to common salt, include the following minerals: sylvine, KC1; carnallite, KC1 MgC12.6H20 (transparent, deliquescent crystals, often red with diffused oxide of iron); kainite, K 2 SO 4 MgSO 4 MgC1 2 6H 2 O (hard crystalline masses, permanent in the air); kieserite MgS04 H20 (only very slowly dissolved by water); besides polyhalite, MgSO 4 K 2 SO 4.2CaSO 4.2H20anhydrite, CaSO 4; salt, NaC1, and some minor components.
For the purpose of the manufacturer of this salt these are assorted into a raw material containing approximately, in Ioo parts, 55-65 of carnallite (representing 16 parts of potassium chloride), 20-25 of common salt, 15-20 of kieserite; 2-4 of tachhydrite (CaC12 2MgC12 12H20), and minor components.
The carnallite produced is dissolved in hot water and the solution allowed to cool, when it deposits a coarse granular potassium chloride containing up to 99% of the pure substance.
Magnesium is found widely distributed in nature, chiefly in the forms of silicate, carbonate and chloride, and occurring in the minerals olivine, hornblende, talc, asbestos, meerschaum, augite, dolomite, magnesite, carnallite, kieserite and kainite.
In later processes, carnallite (a natural double chloride of magnesium and potassium) has commonly, after careful dehydration, been substituted for the single chloride.
Smaller pieces are thrown into a bath of melted carnallite and pressed together with an iron rod, the bath being then heated until the globules of metal float to the top, when they may be removed in perforated iron ladles, through the holes in which the fused chloride can drain away, but through which the melted magnesium cannot pass by reason of its high surface tension.