692 HENRY S. WASHINGTON 
parallel to b (oro), often showing Carlsbad twinning. A few small, 
euhedral, stout prisms of a rather bright-green, pleochroic aegirite- 
augite are also present, but no cossyrite phenocrysts were observed 
in my specimens or noted by Rosenbusch. 
The groundmass is typically holocrystalline, and consists of 
numerous small prisms and anhedra of aegirite and hornblende 
in a colorless base of quartz and alkali-feldspar. Most of the 
aegirite is in the form of euhedral to subhedral prisms, never more 
than o.2 mm. long and about 0.05 mm. thick, and usually much 
smaller, while small anhedral grains are also common. Its color 
is light green, extremely pale in the smaller individuals, and it is 
distinctly pleochroic, especially in the larger and more deeply 
colored individuals: a grass-green, f& and rf lighter yellowish 
green. In the smaller and paler crystals the pleochroism is not 
well-marked. The deeper colored individuals show extinction 
angles c/\a up to 24°, so that they are to be regarded as aegirite- 
augite, while in the small prisms the angle is much less and they 
may be considered to be almost or quite pure aegirite, though 
extremely light in color. 
The hornblendes are by no means as well formed as the 
pyroxenes, and while many of them show a prismatic develop- 
ment, definite crystal faces are lacking, and many individuals are 
small, anhedral grains. Cleavage is not developed. The color 
is a deep chestnut brown and the mineral is highly pleochroic, 
an almost opaque brown and a light hair-brown. Between crossed 
nicols this hornblende often shows a peculiar, brilliant, copper 
color. This hornblende is presumably the cossyrite which forms 
phenocrysts in other Pantellerian lavas, as is suggested by Rosen- 
busch, though the pleochroism is somewhat different. A few 
small, anhedral grains of grayish blue, apparently arfvedsonitic 
hornblende, were seen in some sections, but their presence is 
exceptional. 
The pyroxenes and hornblende are present in about equal 
amount, but there seems to be usually more of the former. They 
are often clustered in somewhat curved, narrow groups, the “den- 
drites” of Foerstner, which produce what might be called a wreath 
texture. The colorless base, seen between crossed nicols and 
