WARREX. — ALKALI-GRAXITES AND PORPHYRIES. 221 



perhaps always, with an earUer formed pyroxene, remnants of wliicli 

 are occasionally to be seen within the aegirite. x\s a rule this earlier 

 pyroxene is almost entirely altered or replaced and what remains is 

 filled with inclusions of fluorite and ferruginous matter. It is almost 

 invariably true that in grains which show this pyroxene, the remnants 

 indicate that it was rounded in form, small in size, and that they are 

 enclosed in or indent the feldspar. In sections of the somewhat less 

 acid phase of the granite from near the porphyry contact on Rattle- 

 snake Hill, grains of a nearly colorless to pale brown pyroxene having 

 the general appearance of augite have been noted, surrounded by a 

 well defined rim of aegirite with a very rapid transition between them. 

 The exact nature of this pyroxene has not been made out. Its ex- 

 tinction 7 on c' is 35° at least ; its double-refraction seems to be lower 

 than common augite. It is probably a calcium-iron-rich pyroxene 

 similar to the pyroxene in the rhombenporphyry. Whatever its 

 original character, it has in general suffered almost complete replace- 

 ment by aegirite, probably during the later stages of the consolidation. 



Occasionally a pyroxene of a deep-green color and otherwise show- 

 ing substantially the properties ascribed to aegirite-augite occur. 

 These appear to have preceded the purer aegirite but to have followed 

 the other variety just referred to. They are thought from chemical 

 considerations to belong to the aegirite-hedenbergite line of mixtures, 

 probably near the aegirite end, although they may be aegirine-augite. 



The aegirite or aegirine-hedenbergite of earlier formation, that is to 

 say the better formed grains, which bear about their margins evi- 

 dences of later growths of the aegirite (analogous to the growths on 

 the hornblende) commonly contain quite abundant, often verj- abun- 

 dant, inclusions. The later formed aegirite rarely contains them. 

 These are, fluorite, in sharply bounded octahedra and rounded grains, 

 sometimes of good size but usually minute, grading down to mere 

 specks: opaque, black grains probably ilmenite; and rarely roundish 

 minute grains of a deep red color, undoubtedly the same as the red 

 mineral forming larger intergrowths with the aegirite and hornblende, 

 and thought to be aenigmatite. (See later.) 



The color of the aegirite in thin-section varies considerably and this 

 variation is often seen in grains that are otherwise optically homo- 

 geneous crystals. The colors commonly observed are as follows: — 

 a, pale to deep green, sometimes with a slight bluish tone: less com- 

 monly almost colorless (usually confined to one part of a grain). (3, 

 pale yellowish-green to almost colorless. 7, pale yellow to pale 

 yellowish-green or almost colorless. In many crystals the whole or 



