Buddington — Natural and Synthetic Melilites. 37 



A statement showing the names of the minerals 

 equivalent in composition to the compounds used in this 

 investigation is given in Table I. 



Table I. 



Formulas of compounds and names of the mineral or synthetic 

 equivalent. 



Compound Mineral equivalent 



2Ca.O.Mg0.2SiOo Akermanite 



2CaO.Al 9 O s .Si(X Gehlenite 



3CaOAl 3 .3SiOo Grossularite 



3CaO.Fe~,0 3 .3SiOo Andradite 



3Na,O.Al,0,.3Si6, Lagoriolite* 



)90"(3CabAl 2 O 8 .3SiO 2 ) 1 Sarcolite 



|10 (3Na 2 O.Al 2 O s .3Si0 2 )f oarcome 



*Prepared and named by Morozewicz. Known only in synthetic prepara- 

 tions. 



Choice of Solid Solutions for Investigation. 



Akermanite and gehlenite had previously been found 

 to form a true binary svstem, but each of the three com- 

 pounds 3Na 2 O.Al 2 3 .3Si0 2 ; 3CaO.Al 2 3 .3Si0 2 ; and 3CaO. 

 Fe 2 3 .3Si0 2 is unstable at or below its melting point, and 

 most of the solid solutions of these compounds with 

 akermanite and gehlenite which were investigated are 

 likewise unstable at their melting point; so that these 

 solutions as a whole, from the standpoint of the phase 

 rule, must be treated as a part of a six-component system 

 embracing their constituent oxides. No attempt has 

 been made in this work to study the solid solutions of 

 2CaO.Mg0.2Si0 2 , 2CaO.Al 2 3 .Si0 2 , and the 3EO.R 2 3 . 

 3Si0 2 compounds as a problem in itself. This can be 

 done only after the many simpler systems embraced 

 within the six-component system of which these solid 

 solutions form a' portion shall have been worked out. 

 Only a few of the possible solid solutions of the com- 

 pounds under consideration have been studied. These, 

 numbering in all about 100, were chosen with the object 

 of obtaining data to explain the melilite group of min- 

 erals as now known from recorded analyses. No effort 

 has been made to determine the nature of the dissocia- 

 tion products of the unstable solid solutions, nor of the 

 other phases present in those mixtures exhibiting 

 inhomogeneity. 



