148 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The smoky and blue crystals are invariably of simple quartz type, prism 

 largely developed with positive and negative rhombohedrons ; in the 

 crocidolite the crystals are doubly terminated. Most of these crystals 

 are deeply etched by solutions which have in some cases dissolved away 

 the whole termination leaving a ragged pitted fragment ; only occasion- 

 ally has the etching been of a sort to leave solution planes and such as 

 were seen were too rough to be measurable. 



The colorless quartz crystals are of a later generation, are small and 

 complexly developed, the following forms having been observed ou the 

 one crystal measured : 



m(lOTO), r(lOTl), z(OlTl), [(4.011), e(50ol), s(ll2l), x(j1(J1), 

 u(31il), (21S1), (53S3), (8.5.T3. 5), (3252). 



The crystal measured was a right-handed one ; left-handed crystals 

 were equally abundant and both types are commonly twinned on the 

 "Dauphind law." 



One very interesting phase of the development of quartz crystals is 

 seen on the surfaces of fractured masses of graphic-granite which have 

 evidently remained after fracture in a solution capable of supplying 

 silica. The quartz of the graphic-granite has grown outward into the 

 surrounding free space, the crystals parallel over considerable areas and 

 with good lustre and a smoky or bluish color but much etched. Some 

 similar but less abundant growth of feldspar and riebeckite could also 

 be observed on the same fragments. Almost always these fragments of 

 regenerated pegmatite are cemented by finely felted crocidolite and the 

 quartz is only revealed when the adhering fibres are removed by 

 vigorous scrubbing with a stiff brush. 



The quartz in the central portion and in the massive parts of the 

 pegmatite all contains strings and sheets of inclusions other than rie- 

 beckite, etc. These are either minute black particles or cavities. In 

 the more freely developed quartz crystals of the pocket the fluid cavi- 

 ties and black inclusions do not seem to be as abundant and often there 

 are almost none at all. The cavities are exactly similar to those in the 

 granite except that they probably reach a larger size on the average. 

 In shape they are round, elliptical, pear-shaped or irregular ; rarely they 

 have been noted with a dihexahedral shape. The cavities commonly 

 contain bubbles which can often be made to move from side to side by 

 turning the stage of the microscope in an inclined position. The largest 

 cavity noted measured 0.02 mm. and the bubble 0.005 mm. Many cav- 

 ities may be seen from .001 to 0.010 mm. in diameter, while the bubbles 

 will in general range from one fifth to one third of the diameter of their 

 cavity. The cavities are often discolored with a ferruginous stain. 



