Manganese mines of St. Marcel, in Italy. 291 



manganese. The amount of this oxidation was determined 

 and gave a basis for calculating the per cent of Mn 2 3 , a blank 

 determination having previously given the trifling amount of 

 oxidation from the air, which was deducted in the calculation. 

 It is probable that the deep red color of the mineral is due to 

 the presence of Mn 2 3 , for it is well known that the higher 

 oxides of manganese have intense coloring power, while that 

 of MnO is very slight. Thus this mineral with about one 

 per cent of the oxides of manganese has a much deeper color 

 than rhodonite with 50 per cent of MnO. 



In calculating the formula it was found that the amount of 

 hydroxy 1 was a little* more than sufficient to unite with the 

 alumina to form the bivalent radical (AlOH) and with the 

 magnesia to form the univalent radical (MgOH). Regarding 

 the (MgOH) 2 and the slight excess of H 2 as isomorphous 

 with K 2 the ratio of the Si0 2 : (AIOIT)O : [(MgOH), K, H] 2 

 O = -893 : 444 : -224 = 4*0 : 1'99 : 1-00 or 4 : 2 : 1. The formula 

 is then R 2 (A10H) 2 Si 4 O n where R equals MgOH, K and very 

 little H, but it seems still better to write this as a metasilicate, 

 HR 2 (A10H)AlSi 4 12 . According to the mica theory of Prof. 

 F. W. Clarke* this composition can also be expressed as a 

 combination of the following molecules in the proportion 1 : 1 



Chemically this mica is distinct from any known species. 

 It is more closely related to lepidolite than to any of the 

 others, being" similar to it in the Si0 2 . A1 2 3 and K 2 per- 

 centages. The composition of both can be expressed as meta- 

 silicates, they are insoluble in acids and before the blowpipe 

 are easily fusible. Although essentially a potash alumina 

 mica, it differs from muscovite in its high Si0 2 and low A1 2 3 

 and in its fusibility, while it is still further removed from 

 biotite and manganophyllite, with which it has been correlated 

 by some authors, by its high silica and insolubility in acids. 

 In a classification, therefore, alurgite should occupy a position 

 near lepidolite and as a distinct species. 



Pyroxene rich in soda, or jadeite. 



The alurgite is associated with and imbedded in a soda rich 

 pyroxene. This occurs as an interwoven aggregate of pris- 

 matic crystals, resembling in structure a rather coarsely crys- 

 tallized jadeite. The material is very tough and shows no 



* This Journal, III, xxxviii, p. 384. 



