Warren — Pegmatite in the Granite of Quincy , Mass. 449 



Art. XLIII. — Note on the Occurrence of an Interesting 

 Pegmatite in the Granite of Quincy ^ Mass.; by C. H. 

 Warren. 



Recent operations in the quarry of Follen Bros, on North 

 Common Hill, Quincy, Mass., have exposed a mass of pegma- 

 tite of such unusual mineralogic interest .that it seems desirable 

 to publish a brief preliminary notice regarding its main fea- 

 tures. The occurrence was first brought to the writer's 

 attention by Mr. F. Wesley Fuller, of West Quincy, and sub- 

 sequently through the courtesy of the owners of the quarry, 

 Professor Charles Falache of Cambridge and the writer were 

 enabled to make a study of the mass in place and to secure 

 abundant material, which is now being studied in detail with 

 the intention of publishing later more fully regarding it. The 

 pegmatite was encountered near the southern side of the 

 quarry about 50 ft. below the surface. It appears to be a 

 huge schlieren of rudely lenticular shape having a maximum 

 thickness of 6 or 7 ft. and a depth and length of about 20 ft. 

 Its position in the granite is nearly vertical. Another much 

 smaller mass is said to have been taken out nearby. 



The contact between the normal granite and the pegmatite 

 is marked by a narrow band ( 2" to 8" ) of granite, finer in 

 texture, poorer in quartz and much richer in hornblende than the 

 normal granite. It shows a well-marked flow-structure. The 

 pegmatite as a whole, although quite variable in texture and 

 composition, still preserves a certain symmetry of structure. 

 Just within the dark band is a broad zone of rather fine-grained 

 pegmatite consisting essentially of orthoclase, quartz, riebeckite, 

 and aegirite. Of these the riebeckite is the most conspicuous 

 mineral, forming long black crystals suggesting somewhat the 

 tourmaline of other pegmatites. In this zone is a considerable 

 amount of graphic-granite, particularly as a narrow band about 

 the margin. The zone also contains considerable amounts of 

 fine-grained material, mineralogically similar to the coarser, 

 scattered irregularly through it. In some parts the pegmatite 

 passes centrally into masses of quartz a foot or more in thick- 

 ness. The quartz along its margins contains large prisms of 

 riebeckite covered with a mantle of segirite and also long 

 acicular crystals of segirite generally arranged in radial clusters. 

 Both of these minerals grow into the quartz from the pegmatite 

 without. Toward what may be considered the main central 

 portion of the mass the pegmatitic material gives way to a fine- 

 grained rock, consisting essentially of orthoclase ( and albite ), 

 segirite and quartz. Still nearer the center the segirite-feld- 



