84 Buddington — Natural and Synthetic Melilites, 



of nephelite and 4 percent of pyroxene. The analysis, 

 recalculated in terms of the assumed components, shows 

 considerable discrepancy. 



The analysis differs from the others in that ferric oxide 

 is high and alumina low, the former evidently replacing 

 the latter. The indices of refraction also differ from 

 those of other specimens obtained by the writer from 

 Capo di Bove. To test for possible inversion phenomena, 

 a sample was heated for 5 days at 1100° ±25°. A few 

 grains are completely inverted but most are cloudy with 

 clear material working in from the edges. Held for 16 

 hours at 1140° ±20° the material is completely inverted 

 to an aggregate of clear bladed grains with lower indices 

 of refraction %— 1.647 and w. e = 1.639. Held for 2 

 hours at 1165° there is a little glass present. 



The composition of this material is such that it does 

 not fall within the limits of the compositions of the syn- 

 thetic mixtures studied, and no comparison can be made. 



Another specimen from the same locality, among those 

 received from Professor Millosevich, has the following 

 indices: na = 1.645 and w e = 1.638. This material was 

 held for one week at 1050° and was then found to consist 

 of an unidentifiable cloudy brown aggregate. 



Another specimen of melilite from Capo di Bove 

 obtained from the U. S. National Museum had the follow- 

 ing indices of refraction: y *w = 1.644 and n e =1.637. 

 The mineral occurs as reddish-brown pseudo-cubic to 

 tabular crystals in a crevice in leucitophyre. Thermal 

 data determined on this specimen are given in Table 

 XXXI. 



The ferric iron rich melilites cannot be recalculated in 

 terms of the components used in the synthetic mixtures 



Table XXXI. 

 Thermal data for Capo di Bove Melilite. no = 1.644 and n<- = 1.637. 



700° 170 hrs. Clear and altered. 



850° 140 hrs. Completely changed to a fibrous aggregate of 



mottled grains with irregular extinction. 

 Indices of refraction 1.648-1.656. 

 1050° 20 hrs. Dense aggregate of birefringent fibers with 



minute dots of high refracting material. 

 Av. n — 1.661. 

 1135° 15 hrs. Similar to preceding, but more highly refracting 



grains more conspicuous. 



