SOURCES AND PREPARATION OF MAGNESIA. 149 



ish in color according to its degree of purity. It is hard and brittle; 

 if cold hydrochloric. acid be dropped upon it no action takes place, 

 but hot acid causes brisk effervescence. 



In composition it is a magnesium carbonate, corresponding to the 

 formula MgCOs. This is equivalent to magnesium carbonate (MgCOs) 

 = magnesium oxide or magnesia (MgO) + carbon dioxide (CO 2). Quan- 

 titatively, pure magnesite (MgCOs) consists of 47.6 per cent magnesia 

 (MgO), 52.4 per cent carbon dioxide (C02). 



Occurrence and origin of magnesite. Magnesite, when in bodies 

 of workable size, occurs commonly in one of three associations, the 

 methods of origin of the deposits being different in each case. The 

 three types of deposits are: 



(1) Magnesite occurs most commonly in the form of irregular veins 

 or pockets in serpentine or other magnesian igneous rocks. In this 

 case the magnesite has been formed as a decomposition product aris- 

 ing from the decay of the igneous rock. 



(2) Magnesite occurs in the form of beds associated with deposits 

 of rock salt, gypsum, etc. In this case the magnesite deposit has un- 

 doubtedly originated by direct deposition of magnesium carbonate 

 from bodies of concentrated saline waters. 



(3) Magnesite also occurs in the form of beds interstratified with 

 shales, limestones, etc. Magnesite deposits of this type are commonly 

 ascribed to the replacement of the lime (in a limestone) by magnesia 

 carried in by percolating waters. This may be true in some cases, but 

 such deposits may also have originated by direct deposition, as described 

 under (2), above. 



In most of the workable magnesite deposits noted below, however, 

 the first method of origin is the true explanation. 



Distribution of magnesite deposits. The magnesite deposits now 

 exploited on a sufficient scale to be of commercial interest occur in 

 Austria, Germany, Greece, Hungary, India, and the United States. 

 Workable deposits also occur in Canada, but as yet have not been suffi- 

 ciently opened up to determine their commerical importance. 



Foreign localities. The principal Austrian magnesite deposits are 

 near Mittendorf, in Styria, and near Tolsvar, in the province of Minsan, 

 Hungary. The Styrian magnesite averages about 88 per cent mag- 

 nesium carbonate with about 8 per cent of silica, alumina, and iron 

 oxide. The Hungarian product is a purer magnesite, carrying 92 to 

 95 per cent magnesium carbonate, with 3 or 4 per cent iron oxide. 



In Germany the deposits now worked occur near Kosewitz and 

 Frankenstein, in Silesia, and are principally worked in connection with 



