Buddington — Natural and Synthetic Melilites. 69 



tion of water, stated in terms of its constituent molecules, 

 and compared with the calculated molecules in a mixture 

 composed of 76 percent 2CaO.Al 2 3 .Si0 2 , 17 percent 

 2CaO.Mg0.2Si0 2 , 4 percent 3CaO.Fe 2 3 .3Si0 2 , 2.3 per- 

 cent 2CaO.Fe0.2Si0 2 and 0.7 percent 3(Na,K) 2 O.Al 2 3 . 

 3Si0 2 . 



When recalculated in terms of the components already 

 described it is found to consist roughly of 76 percent 

 gehlenite, 17 percent akermanite, and 7 percent ferric and 

 ferrous compounds. A comparison of its properties with 

 those of artificial gehlenite having the same ratio of aker- 

 manite to gehlenite, but free of iron compounds, is given 

 in Table XX. It will be seen that the agreement is very 



Table XX. 



Comparison of properties of natural Gehlenites with those of similar artificial 



preparations. 



Natural Artificial Natural Artificial Natural Artificial 

 Locality Valardena, Monzoni, Tulare Co., 



Mexico. Italy. Calif. 



Analyst E. T. Allen. Eammelsberg. E. V. Shannon. 



Gehlenite 76 82 58 67 66 70 



Akermanite 17 18 28 33 28 30 



Iron Compounds . . 7 14 6 



mo 1.639 1.639 1.662 1.659 1.660 1.660 



n e 1.633 1.6324- 1.657 1.655 1.657 1.656 



Birefringence 006 .007' .005 .004 .003 .004 



Density 3.039 3.024 3.008 3.02 3.01 



Solidus 1475°±20° 1504°±5° 1375°±25° 1462°±5° 



Liquidus 1555°±20° 1556°±5° 1500°±20° 1530°±5° 



Remarks : The data on the Velardefia gehlenite were determined by F. E. 

 Wright on the same sample as that analyzed. The optical data and thermal 

 data for the Monzoni gehlenite were determined by the writer on a sample 

 different from that analyzed by Eammelsberg. The optical data for the 

 California gehlenite were determined by the writer on the same sample as 

 that analyzed by Shannon. 



close, and would be even closer if the values of the min- 

 eral were corrected for the presence of iron compounds 

 which tend to raise the indices of refraction, raise the 

 density, and lower the solidus and liquidus. In order 

 to ascertain whether the mineral gehlenite would invert 

 to some different form at higher temperatures, a charge 

 was heated for 16 hours at 1450° without showing any 

 change in indices of refraction. A second charge was 



