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



spar rock becomes much coarser in grain, at the same time 

 full of cavities aud so loosely coherent that it may be easily 

 broken up. The minerals, particularly the segirite, project out 

 into the open spaces. Quartz is now less abundant than 

 elsewhere, but it is possible that the cavernous texture is in 

 part due to the dissolving out of original quartz. The feld- 

 spars are well formed, about equi-dimensional, and will perhaps 

 average about the size of a grain of corn, although they vary 

 from this average considerably in either direction. They 

 appear to be chiefly orthoclase mantled with a thin cover of 

 albite : albite also forms in small separate crystals. The 

 gegirite is dark green in color and in general forms very 

 irregular, prismatic, often tapering crystals which seem to 

 consist of an aggregate of slender prisms. Many, however, 

 exhibit a well-developed prism zone (forms 100, 110), are 

 often twinned ( on 100 ), and not infrequently attain a length 

 of several centimeters. Terminal faces occur but are rare 

 and even on the better crystals are apt to be curiously irregular. 

 Some of the crystals are deeply pitted by solution. In addition 

 to the minerals named there occurs quite abundantly another 

 mineral which appears to be the rare fluo-carbonate of lime 

 and the cerium earths, synchysite, described by Flink from 

 Greenland, wdiere it occurs with a mineral association similar 

 to the Quincy occurrence. The synchysite occurs generally in 

 slender, amber-colored prisms terminated by a basal plane 

 often truncated by the forms of a hexagonal pyramid or 

 rhombohedron or both. The prism zone is deeply striated and 

 has a marked oscillatory development. Zircon crystals are 

 closely associated with the synchysite and are of frequent 

 occurrence. Minute crystals of ilmenite and hematite are 

 occasionally found ; also a few minute, black crystals of some 

 as yet unidentified titanium mineral, and two or three small 

 crystals strongly resembling scheelite. Quartz crystals are 

 also found in the pockets. These are more abundant toward 

 the center, while in and along a line of large central pockets 

 the quartz crystals are very numerous and attain a large size. 

 The quartz is in part at least of later age and contains many 

 inclusions of segirite and secondary hornblende (see later). 



The upward extension of this line of large central pockets 

 presents several features of unusual interest. Here are 

 found undoubted fragments of the pegmatitic material first 

 described. Although generally smaller they have been noted 

 as large as 6 or 8 inches in average diameter and are imbedded 

 in a compact, beautifully silky, grayish-blue crocidolite. 

 These pockets also contain great numbers of quartz crystals and 

 a smaller amount of nuorite, both imbedded in crocidolite, 

 which in fact practically fills up the otherwise free spaces. A 



