WARREN. — ALKALI-GRANITES AND PORPHYRIES. 247 



the margins of the enlarged feldspar phenocrysts which served as 

 points of attachment and sometimes entirely surround them. The 

 smaller microperthitic feldspars of phenocrystalline age with their 

 enlargements are even enclosed by a single group along with ground- 

 mass microperthite and quartz (as shown in Figure II, Plate 1). 

 The hornblende, with the possible exception of the massive centers, 

 obviously belongs to the groundmass period of crystalhzation. 



In relatively thick sections or with crushed material, the hornblende 

 possesses a prevailingly dark-blue or greenish-blue color. In good 

 thin-sections, however, the characteristic color is a deep green or a 

 bluish-green and the purer blue tones appear about the periphery or 

 in streaks, and only rarely makes up any considerable portion of the 

 more massive parts. The other characteristic ray (across the cleavage 

 in 010 sections) is colored light yellow, light yellowish-green or light 

 brownish-yellow. The extinction, in part, is that of riebeckite, but as 

 in the granite, the extinction of the greener hornblende is much larger 

 (ca 35°), indicating an alkali-hornblende, probably a cataphorite. 

 The optical elongation is very difficult to determine owing to the deep 

 colors and low double refraction but is negative for the blue type and 

 probably positive for the catophorite. 



The texture of the hornblende is well described as "spongiform," 

 or more accurately, as domoikic with relatively fine to coarse xeno- 

 crysts. The feldspar and quartz xenocrysts show about the same 

 range of sizes. They are irregular to tabular in hal)it while the quartz 

 xenocrysts are commonly round. 



Aegirite is the most abundant pyroxene but some other variety is 

 present, of augitic appearance. The augitic pyroxene occurs in cer- 

 tain of the feldspar phenocrysts and also in the form of larger 

 crystals in the groundmass, often surrounded by the hornblende (see 

 Figure 1, Plate 1). It has sometimes a pale brown color but is 

 usually a pale greenish-yellow. Rarely the augite material extends 

 to a sharply marked line about which is a rim of deep-green aegirite. 

 More often the augite appears as such, only at the center, and is suc- 

 ceeded outwardly by an indefinitely bounded green, aegiritic looking 

 material. The depth of color increases toward the margin. The 

 extreme edge appears to be aegirite. Again no augite can be seen, 

 but the green to deep-green material "with, however, the habit of the 

 augite, forms a core which is indefinitely bordered by aegirite. Twin- 

 ning on a, 100 occurs as do also zonal structures, but the latter lack 

 sharpness. The aegiritic material is often finely granular, and may 

 include fluorite grains, and much indeterminate dust. Occasionally 



