H. S. Washington — New Leucite Rock. 41 



Leucite anhedra, 80 per cent or more, equant, about 3-5 

 mm., usually containing few inclusions. Pyroxene, in 

 small black prisms, and garnet, in small black grains, 

 not more than 5 per cent each. Interstitial glass cement, 

 about 5 per cent, may be present, and negligible amounts 

 of other minerals possibly present. 



Microscopic characters. — Percrystalline, megaporphy- 

 ritic, persemic, mediophyric. 



Leucite: megaphenocrysts, 80 per cent or more, usu- 

 ally clear, twinned, few inclusions, not necessarily regu- 

 larly arranged. Pyroxene : acmite-diopside, 5 per cent 

 or less, usually prismoids and about 1 mm., green, pleo- 

 chroic. Melanite : 5 per cent or less, small anhedra. 

 Biotite, magnetite, apatite : 1 per cent or less of any may 

 be present. Base : about 5 per cent, glass, usually color- 

 less, with or without microlites. 



Chemical composition. — Approximately that given on 

 page 37 above. Type specimen from near San Carlo, 

 Eocca Monfina Volcano, Italy. 



Garnet in Italite. 



Titaniferous melanite. — By means of a magnet 0-0639 

 gram of the small grains of garnet was isolated from 

 5-25 grams of the rock powder, practically entirely free 

 from pyroxene and magnetite. It was sufficiently pure, 

 at least, to establish the general composition and char- 

 acter of the mineral, and a partial analysis was made of 

 this portion, with the results given below. Because of 

 the very small amount of material available, ferrous and 

 manganous oxides, the alkalies, and water could not also 

 be determined. The sodium carbonate melt was colored 

 a decided blue-green and, judging from the depth of this 

 in connection with the amount of substance, it was esti- 

 mated that about 0-10-0-20 (or possibly more), per cent 

 of MnO was present. 



SiO, 29-7 -496 



TiO, 8-7 -108 



A1 2 3 8-1 -080 



Fe,0 3 23-6 -147 



MgO 0-7 -017 



CaO 28-8 -515 



•604 

 •227 

 •532 



99-6 

 Analysis of melanite from italite, Eocca Monfina. 



