Warren — Pegmatite in the Granite of Quincy, Mass. 451 



considerable amount of some other secondary hornblende 

 occurs in the form of exceedingly delicate, black needles in 

 the crocidolite, penetrating the quartz, and in cavities in 

 the pegmatite fragments. The large riebeckite crystals in these 

 fragments are often partially or almost completely eaten out 

 and the cavities then formed may contain later formed quartz 

 and hornblende needles. -On one or more faces of the frag- 

 ments there is usually found a later growth of quartz which 

 took the form of a direct addition to the original quartz of 

 the fragment. The quartz crystals of the pockets vary greatly 

 in size from exceedingly minute individuals to crystals upwards 

 of a foot in length and 3 or 4 inches thick. Many of 

 the smaller crystals are very rich in planes although most 

 of them are curiously irregular, distorted, their surfaces 

 covered with etch-pits, or what in other cases resemble growth- 

 forms. Some crystals have been broken and recemented. 

 Beside the included needles of black hornblende practically all 

 of the quartz is crowded with the crocidolite, which gives it a 

 peculiar bluish color often very attractive. The fluorite has a 

 dark purple color, is beautifully phosphorescent when heated 

 and forms generally in distinct octahedral crystals sometimes 

 an inch or two in diameter. It too has been acted on by 

 some solvent. All stages of solution may be seen to that. in 

 which only the mold of the crystal remains containing a mass 

 of fibers originally included in the nuorite. In one large 

 mass of quartz adjoining the line of pockets several good- 

 sized masses of granular galena carrying a little sphalerite and 

 chalcopyrite were found, associated with nuorite and crocid- 

 olite. 



The pegmatite as a whole appears to be a segregation from 

 the granite characterized by unusual richness ( compared 

 with the granite ) in certain constituents, notably fluorine, the 

 rare earths, lead, zinc and probably quartz. The crystallization 

 seems to have taken place from the margin inward with cer- 

 tain progressive changes in texture and mineral composition, 

 the central portions becoming as a result increasingly richer in 

 silica, fluorine, the rare earths and the aegirite molecule. The 

 central cavities are thought to be chiefly mariolitic in char- 

 acter, thus allowing a free crystallization. Before the com- 

 pletion of the crystallization there appears to have been a 

 movement in the mass as a whole which resulted in more or 

 less breaking and the formation of fragments found in the 

 pockets. The flow-structure in the dark marginal band about 

 the pegmatite bears out this idea of movement. The residual 

 liquor in the central pockets under the changed physical con- 

 ditions exerted a solvent action on some, perhaps all of the 

 minerals already formed, and also effected chemical or molec- 



