368 P. Eskola — Silicates of Strontium and Barium. 



Some General Considerations Regarding the Relations of the 

 Alkaline Earth Compounds. 



"With the exception of some rare titanosilicates, the 

 only natural anhydrous silicates of barium known are 

 barium feldspar, or celsian, BaAl 2 Si 2 8 , notable for its 

 isomorphism with potash feldspar, barylite, Ba 4 Al 4 Si 7 - 

 24 , and taramellite, Ba 4 Fe"Fe" / 4 Si 10 O 31 . Hydrated 

 silicates are more numerous, mostly belonging to the 

 zeolite group, namely: brewsterite, H 4 (Sr,Ba,Ca)Al 2 Si 6 - 

 1? + 3H 2 0, harmotome, H 2 (K 2 ,Ba)Al 2 Si 5 15 + 4H 2 0, 

 edingtonite, BaAl 2 Sio0 10 + 3H 2 and wellsite (Ba,Sr,Ca,- 

 K 2 )Al 2 Si 3 O 10 + 3H 2 0. Micas sometimes contain appre- 

 ciable amounts of barium. 



No strontium silicates are known as minerals, though 

 this element, in smaller quantities, is contained in some 

 rock-forming feldspars, probably plagioclases (cf. p. 365), 

 and in hancockite, a lead-epidote, and in zeolite minerals 

 heulandite, H 4 (Ca,Sr)Al 2 Si 6 18 + 3H 2 0, and wellsite 

 and brewsterite, named above. 



The present study adds some information concerning 

 the isomorphous relations of a number of other silicates 

 of strontium and barium. Thus the compound BaO. 

 2Si0 2 which was suggested by Bowen (loc. cit.) to be 

 isomorphous with the potassium disilicate studied by 

 Morey and Fenner, 34 has now been found to be also iso- 

 morphous with 2Ba0.3Si0 2 . A strontium metasilicate 

 was found to be isomorphous with a form of calcium 

 metasilicate, and a strontium orthosilicate is probably 

 isomorphous with either the a or the p form of calcium 

 orthosilicate. A strontium feldspar was found to be 

 probably isomorphous with the lime feldspar, anorthite, 

 which is also isomorphous with a soda feldspar. 



Now taking into account all the compounds of the alka- 

 line earths, silicates as well as others, we may discrimi- 

 nate, according to their isomorphous relations to com- 

 pounds of other elements, at least four different classes : 



(1) Calcium, strontium, and barium compounds iso- 

 morphous with each other (all or two of them) and also 

 isomorphous with lead compounds. Examples : The 

 tetrahedral-pentagondodecahedral nitrates of Ca(?), Sr, 

 Ba, and Pb. The orthorhombic carbonates, aragonite, 

 strontianite, witherite, and cerussite. The sulphates, 



34 G. W. Morey and C. N. Fenner, J. Am. Chem. Soc, 36, 215, 1914. 



