to Calcium, and Magnesium Metasilicates. 13 



Diopside from 



Ham Island, 



Alaska 



Si0 2 54-65 



Fe.O, -13 



CaO 25-27 



MgO 18-78 



Na o _ -03 



K o -07 



HO 1-45 



Cal. to the 



Cal. for 



anhydrous 



CaSiO-3 



condition 



MgSiOs 



55-46 



53-63 



•13 



. _ _ , 



25-64 



25-82 



19-06 



18-55 



•03 







•07 















100-38 100-39 100-00 



When diopside is prepared by melting together lime, mag- 

 nesia and silica in the proper proportions, it crystallizes readily, 

 bat not so rapidly as its constituents calcium and magnesium 

 silicates, forming a dense white homogeneous mass with con- 

 spicuous cleavage. The optical constants, a full account of 

 which is given in the second part of this paper, leave no room 

 for doubt of the identity of the substance. 



Measurable crystals was prepared by crystallizing this prod- 

 uct from molten calcium chloride-Le Chartier's method.* This 

 may be very conveniently done in platinum as described in a 

 previous paper on magnesium silicate. f It is not possible, 

 however, to perform the operation in hydrochloric acid gas, as 

 was there done, for the diopside is then decomposed into cal- 

 cium chloride, tridymite and magnesium pyroxene. The last 

 two products were identified optically without difficulty. The 

 calcium chloride should first be melted in the sealed crucible, 

 traversed by a stream of dry hydrochloric acid gas. Then 

 after the crucible has been cooled and the hydrochloric acid 

 replaced by dry air, the crucible is unsealed and the silicate 

 quickly introduced. In this operation some moisture doubt- 

 less gets in. Before heating again, dry indifferent gas is 

 introduced. The crucible is heated for a number of days, the 

 entering and exit tubes being guarded by driers. When the 

 operation is completed, the excess of calcium chloride is 

 removed by water. The product is usually in the form of 

 transparent crystals of rhombic habit which sometimes attain 

 to dimensions of several millimeters. The planes are often 

 slightly coated with a thin film of what is probably calcium 

 hydroxide, which doubtless comes from the decomposition of 

 calcium chloride by the water vapor which could not be 

 entirely excluded. It gives a strong alkaline reaction and may 

 be readily removed with a little dilute HC1. Analysis shows 

 that no lime is dissolved by the crystals, though they are not 

 quite free from chlorine. 



* Comptes Eendus, lxvii, 43, 1868. fThis Journal, xxii, 389, 1906. 



