Biiddington — Natural and Synthetic Melilites. 65 



attempt to correlate these data with those derived from 

 studies of the minerals. The optical data suggest them- 

 selves as being the best for this purpose, but unfortu- 

 nately, with respect to this group of minerals, such data 

 are meager and in only a few cases have both the optical 



Fig. 11. 



70 3Ca0«Fe 2 3 -3Si0 2 

 20 2CaO-Al 2 3 -S0 2 

 10 3MaO«Al 0.3 SO 



• COMPLETE SOLID SOLUTION 

 O INCOMPLETE SOLID SOLUTION 



70 3Ca0«Al 2 3 *3Si0 2 

 20 2CaO*Al 2 3 *Si0 2 

 10 3Ma 2 0*Al 2 3 *3Si0 2 



70 2Ca0«Kg0«2S0 2 



20 2CaO*Al 2 3 *Si0 2 wt percent 



10 3Na 2 0«Al 2 3 «3$i0 2 



11. — Triangular concentration diagram showing compositions of prepara- 

 tions investigated. Lines connecting similar indices of refraction have been 

 plotted for those mixtures which show complete homogeneity just below 

 the beginning of melting, or the point of dissociation, and above 1100° (the 

 lowest temperature at which experiments were made). 



data and the chemical analysis been given for the same 

 specimen. This is strikingly true of the best known 

 melilites, those of Italy. 



Partially to remedy this defect, specimens of Italian 

 ferric iron-rich melilites, and of gehlenites, humboldt- 

 ilites, sarcolite, and fuggerite were obtained for purposes 

 of study from the U. S. National Museum and from 



Am. Jour. Sci.— Fifth Series, Vol. III. No. 13.— January, 1H22. 

 5 



