Buddington — Natural and Synthetic Melilites. 81 



Table XXVIII. 

 Humboldtilite from Colorado. 



Original Analysis Calculated Differ- 



analysis reduced. Mol. molecules ence 



SiO, 42.07 43.80 7263 6830 —433 



TiO., 20 ,20 25 — 25 



Al,6 3 10.30 10.52 1052 1189 +137 



CaO 35.41 34.64 6174 6254 +80 



MgO 4.15 4.32 1072 1245 +173 



Fe-A 50 .52 33 39+6 



Feb 2.18 2.27 315 ) q9Q '. -. 



MnO 16 .16 22 J 6 ^ + i 



Na,0 3.24 3.37 543 576 + 33 



K,6 Trace 



P,0 5 82 



CO., 90 



H 2 6 47 



100.40 100.00 



Mixture 

 weight percent. 

 45 3CaO.Al,0 3 .3SiO, 

 34 2CaO.MgO.2SiO, 

 10 2CaO.FeO.2SiO, 

 9 3(Na,K),O.Al,6 3 . 



3SiO, 

 2 3CaO.Fe,0 6 .3SiO, 



with pyroxene, perofskite, and apatite. Its density is 

 2.98. Table XXVIII gives a statement of the original 

 analysis, the analysis reduced to 100 with elimination of 

 water, apatite, and calcium carbonate, the analysis stated 

 in terms of its constituent molecules, and for comparison 

 the calculated molecules of a mixture of assumed com- 

 ponents most closely approximating the natural mineral 

 in composition. This analysis does not lend itself 

 readily to recalculation in terms of the components 

 considered. 



A comparison of its optical properties with those 

 of a similar synthetic preparation is given in Table 

 XXIX. The agreement here, again, is as close as could 

 be expected. 



Table XXIX. 



Comparison of properties of Colorado Humboldtilites with those of similar 

 synthetic preparations. 



Components. Natural. Artificial. 



Akermanite 34 40 



3CaO.AlA.3SiO, 45 50 



3Na,O.Al,0,.3Si6, { Q n n 



3K 2 6.Al,6 3 .3SiO, ) y iU 



3CaO.Fe 2 3 .3SiO, 2 



Ferrous minerals 10 



no 1.632+ 1.630 



n € 1.626— 1.627 



Birefringence 007 .003 



Am. Jour. Scl— Fift.s Series, Vol. Ill, No. 13.— January. 1922. 



