36 H. 8. Washington — New Leucite Rock. 



crowded with minute (0-01-0-05 mm.) spheroidal inclu- 

 sions, each of which is composed of glass containing still 

 smaller granules of a colorless, birefringent substance, 

 of rather high refractive index. 



Pyroxene is not abundant, and occurs mostly between 

 the leucite crystals, but to some extent partly in these 

 and partly in the glass. It is an "aggirite-augite," or 

 rather an acmite-diopside, as a recent study of the aegi- 

 rite group (soon to be published) by Dr. Merwin and 

 me has shown to be true of most of the so-called segirite- 

 augites. The crystals are subhedral, generally with 

 some prismatic planes. The color is a rather dark yel- 

 low-green, and the mineral is but slightly pleochroic, 

 varying from a greenish yellow, Ridgeway's 3 "oil- 

 green" (27/c) to a greenish yellow-green, Ridgeway's 

 "grass-green" (33k). The extinction angle is about 

 40° ; a = 1-710-1-715 and y = 1-752 ; and 2V = ca. 70°, 

 these data having been kindly determined by Dr. Merwin, 

 to whom I am much indebted for this and other deter- 

 minations. It was not practicable to isolate sufficient 

 pyroxene in a pure condition for a satisfactory analysis,. 

 so that study of its chemical composition must be de- 

 ferred until more abundant material is in my hands. 



In decidedly less amount than the pyroxene prismoids 

 are small anhedral grains of a deep red-brown, isotropic 

 mineral, with the high refractive index, n = 1-94, as de- 

 termined by Merwin. A partial analysis, made on a 

 very small amount of material, shows that this is a 

 titanif erous melanite, similar to that found in lavas else- 

 where, as at Tavolato and Frascati at the Alban Volcano. 

 It will be discussed, and the analysis given, at the close 

 of this paper. 



There are a few small, thick tables of a dark, reddish, 

 pleochroic biotite, most of them in the segirite, some small 

 grains of magnetite, and the rare colorless apatite prisms 

 mentioned above. No hauyne nor noselite was seen. 



A colorless glass base occurs in small amount, inter- 

 stitial between the leucite crystals. It shows no perlitic 

 cracks, but contains some small, spherical bubbles, and 

 occasionally (in patches) small (0-05-0-10 mm.) black, 

 opaque, rounded grains, that are probably magnetite, as 

 the glass near them in places is stained yellow. For the 

 most part the glass is crowded with very minute (0-001- 



3 K. Ridgway, Color Standards and Nomenclature. Washington, 1912. 



