Buddington — Natural and Synthetic Melilites. 85 



without discrepancies of some magnitude. The chemical 

 analyses by Zambonini of two ferric iron rich melilites 

 from Capo di Bove are given in Table XXXII. The 



Table XXXII. 



Comparison of analyses of ferric iron rich melilites by Zambonini with 

 calculated composition of synthetic mixture. 



I. . II. III. 



SiO, 40.14 39.20 38.38 



AI063 6.47 7.56 5.90 



Cab 32.98 43.18 34.13 



MgO 6.33 6.41 6.64 



FeX> s 9.95 11.34 10.98 



Feb 53 



Na.0 2.18 2.21 3.97 



K 2 " 1.49 1.45 



H 2 27 .21 



Ti0 2 ,MnO Trace Trace 



100.34 100.56 100.00 



I. Yellow melilite from Capo di Bove. 

 II. Brown melilite from Capo di Bove. 

 III. Calculated composition of mixture of 45 percent 2CaO.Mg0.2Si0 2 , 

 35 percent 3CaO.Fe->0 3 .3Si0 2 , 10 percent 3Na 2 O.Al 2 3 .3Si(X and 10 percent 

 2CaO.Al 2 3 .Si0 2 . 



composition of a synthetic mixture composed of 45 per- 

 cent akermanite, 35 percent andradite, 10 percent 3Na 2 0. 

 Al 2 3 .3Si0 2 , and 10 percent gehlenite is given for com- 

 parison. The crystallized synthetic mixture of this 

 composition has the following indices of refraction: 

 n u — 1.676 and n E = 1.658. These indices are conspicu- 

 ously higher than those of the natural melilites of similar 

 composition, if we may assume that our mineral was 

 similar to those analyzed by Zambonini. The natural 

 mineral, when heated at 850°, changes to a fibrous aggre- 

 gate of higher indices of refraction and the actual inver- 

 sion or dissociation point may be much lower. The syn- 

 thetic preparation and the natural mineral therefore do 

 not correspond. 



The following results show that the synthetic prepara- 

 tions may have different phases. A glass consisting of 

 10 percent 3Na 2 O.Al 2 3 .3Si0 2 , 67.5 percent 2CaO.MgO. 

 2Si0 2 , and 22.5 percent 3CaO.Fe 2 3 .3Si0 2 was held for 

 1 month at 700° ± 25°. The result was an aggregate 

 of minute spherulites with blue gray fibers with an aver- 



