76 Buddington — Natural and Synthetic Melilites. 



in composition and character to that first described from 

 Vesuvius. They differ essentially from the mineral orig- 

 inally called melilite in having relatively less ferric iron 

 and in some cases a relatively greater percentage of 

 ferrous iron, and a larger percentage of the 3CaO.Al 2 3 . 

 3Si0 2 molecule. 



Table XXIII. 

 Chemical analyses of Humboldtilite from Monte Somma, Vesuvius. 



A B CD E 



SiO, -. 39.86 41.69 40.36 40.69 41.09 



Al 2 6 3 11.37 9.59 12.04 10.88 10.93 



FeX> 3 50 .76 .75 4.43 3.40 



FeO 1.78 3.75 1.53 



MgO 7.63 5.32 6.56 5.75 5.87 



CaO 35.58 32.82 34.71 31.81 34.78 



Na,0 2.13 4.76 3.34 4.43 3.40 



K,6 S2 .68 .30 .36 .68 



HX>4- 0.49 0.29 0.79 



H 2 0— 0.10 0.05 0.13 .24 



Total 100.26 99.71 100.51 98.35 100.39 



Density 2.975 2.925 2.92 to 



2.95 



A. White crystals, thickly tabular parallel to base, occurring in vugs and 

 as interstitial material in Vesbite, a lava composed of about 65% leucite, 

 18% humboldtilite, 20% pyroxene, 2% magnetite. See Jour. Wash. Ac. Sci., 

 vol. 10, No. 9, 272, 1920. Washington, analyst. 



B. Crystals and interstitial material in vesbite. Crystal habit is tabular 

 parallel to base, combination of 1st order prism and base modified by 2d 

 order prism. Washington, analyst. 



C. Crystals occurring in pockets in limestone masses included in leucitite. 

 Crystal habit thick tabular parallel to base ; combination of 1st order prism 

 modified by ditetragonal prism and base. Colorless to transparent. Wash- 

 ington, analyst. 



D. Analysis by Damour, Dana's System of Mineralogy, 6th edit., p. 475. 



E. Analysis by Bodlaender, Neues Jahrb., 1893, 1, p. 17. 



Monte Somma Humboldtilite. — In Table XXIII are 

 given the chemical analyses of three specimens of hum- 

 boldtilite selected by the writer and analyzed by Dr. H. S. 

 Washington. Two analyses made by other analysts are 

 included for comparison. A noteworthy difference lies 

 in the fact that the iron as found by Dr. Washington is 

 for the most part in the ferrous state, whereas the condi- 

 tion of the iron as reported by most of the other analysts 

 is the ferric oxide, the two oxides not having been sepa- 

 rately determined. 



