WARREX AND PAL-\CUE. — QUINCY PEGMATITES. 131 



should in fact be properly termed aegirite-riebeckite crystals. They 

 often contain granular masses of dark purple tiuorit© mixed with zircon, 

 ilmenite, and quartz, besides decomposition products, chiefly ferrugi- 

 nous in character, which are apt to discolor that portion of the crystal 

 in which they occur. With the coarser material of this zone is 

 more or less fine-grained material. This corresponds to the more 

 abundant fine material to be noted later in connection with the descrip- 

 tion of the Fallon quarry pegmatites, and consists largely of quartz, 

 microcline, aegirite, zircon, tluorite, ilmenite, a few grains of a nearly 

 colorless, isotropic mineral of very high refractive index thought to 

 be beckelite (see later), besides various secondary products. The 

 larger feldspar grains lying about these fine-grained, zircon -rich areas, 

 are particularly apt to contain small, slender prismoid crystals of 

 albite which are probably later crystallizations, and are connected 

 with pneumatolitic processes. Parts of this fine-grained material are 

 very rich in zircon, and ilmenite (and hematite ?). Alteration develops 

 in this material (see later) a red or brownish-red stain which produces 

 in the rock the appearance of metallic spot^. Occasional crystals of 

 zircon attain macroscopic size and are well developed crystallographi- 

 cally. Thin sections of these zircon-rich portions show an interesting 

 relationship between the quartz and zircon. There is a marked ten- 

 dency on the part of the zircon to form granular intergrowths with 

 quartz. In some instances relatively large zircon grains showing 

 simultaneous extinctions are found enclosed in a (juartz grain. In 

 most ca.ses, however, both minerals are granular. The zircon tends 

 to form closely packed aggregates ; the grains may have a parallel 

 orientation, although they are often separate and show a more or less 

 well-defined crystal outline. The quartz also shows a tendency to 

 a parallel arrangement of its grains. The (juartz-zircon intergrowths 

 are commonly bounded as a whole by a crystal outline, apparently 

 that of a zircon crystal having a short prism with the unit pjTamid 

 termination. This outline is usually marked by a string of small 

 zircon grains. The quartz surrounding these areas has fi-e(iuently a 

 distinct orientation of its crystals per])endicular to the boundaries of 

 the area, a feature that, indeed, may be obscurely visible in the hand 

 specimen. The areas often penetrate adjoining feldspar grains and 

 are closely associated with aegirite. Fluorite, ilmenite, and ferrugi- 

 nous alteration products are also quite abundantly mixed with the 

 zircon and fpiartz. These zircon-cjuartz groujjs evidently belong to 

 the i)neumatolitic i)erio(l and represent, it is believed, zircon crystals 

 which subsequent to their formation sufiered more or le.ss recrystal- 

 lization, replacement by ({uartz, and perhaps granulation. Figure 



