P. Eskola — Silicates of Strontium and Barium. 369 



celestite, barite, and anglesite, form an isomorphous 

 series which excludes calcium sulphate. Among silicates 

 we note the group of hancockite and epidote, and we have 

 now found that the metasilicates form an isomorphous 

 series to which belong only the calcium and strontium, 

 but not the barium metasilicate. 35 



(2) Calcium and strontium (also barium!) com- 

 pounds isomorphous with each other and also isomor- 

 phous with sodium compounds. Example: Anorthite 

 and strontium anorthite. 



(3) Barium compounds isomorphous with potassium 

 compounds. Example : Barium disilicate. Among the 

 natural silicates named above, celsian and harmotome 

 are representatives of this class. 



(4) Calcium compounds isomorphous with corre- 

 sponding compounds of magnesium, ferrous iron and a 

 number of other elements, but not with those of barium or 

 strontium. Example : The rhombohedral carbonates, 

 calcite, magnesite, siderite, etc. 



It seems to be a rule that in the compounds in which 

 the lime may possibly be replaced by magnesia and 

 ferrous oxide, it can not be replaced by strontia or baryta. 

 Thus it was found in the present work that there are no 

 strontium or barium compounds analogous to diopside, 

 CaO.Mg0.2Si0 2 . 



Accordingly we find, in nature, strontium and barium 

 compounds forming mix crystals with lime and alkali 

 minerals, but not with ferromagnesian, although the 

 latter may contain calcium. In other words, these 

 elements are likely to be found in salic rather than in 

 femic rocks, a circumstance that is really very striking 

 in their distribution in the igneous rocks. 



The authors of the so-called quantitative classification 

 of igneous rocks make a distinction between salic and 

 femic lime. Now these terms gain added significance, as 

 we find that only the salic but not the femic lime may be 

 replaced by strontia. 



It may be of interest, for the sake of comparison, to 

 present together some important properties of the 

 members of some well known simple compounds of the 

 three alkaline earth metals. 



33 Bourgeois (Ann. chim. phys., 29, 445, 1883) records a lead metasilicate 

 of a similar appearance to those of calcium and strontium. 



