450 PROCEEDINGS OF THE NATIONAL MUSEUM. v 



Analysis of gedrite from Chesterfield, Massachusetts. 



SiOj 49.66 



AljOs 6.74 



Fe,0, 1. 23 



FeO 18. 09 



CaO 3. 38 



MgO 18.62 



MnO . 05 



H,0 1. 56 



99. 33 

 The catalogue number of this material in the Museum collections 

 is 93699. 



AN OCCURRENCE OF THE BUCHOLZITE VARIETY OF SILLIMANITE 

 IN PEGMATITE. 



The specimens upon which the following brief descriptions are 

 based (Cat. 93704, U.S.N.M.) were collected by the writer in the 

 ftown of Russell, Massacliusetts. The locality is on the Woronoco- 

 Blandford road, about 1 mile west of the village of Woronoco, at 

 lower Salmon Falls. The area here is occupied by a silvery mica 

 schist known as the Goshen Schist,^ much intruded by long, narrow 

 dikes of a medium-grained granite pegmatite of ordinary composi- 

 tion devoid of conspicuous accessory minerals. At the particular 

 point where the sillimanite occurs there are several dikes 8 inches 

 to a foot in width, composed solely of quartz and muscovite. The 

 sillimanite forms a sinuous sheet occupying a central suture in these 

 dikes and varying from 1 millimeter to 2 centimeters in thickness. 

 In other wider dikes the middle is occupied by feldspar in which 

 the sillimanite occurs in small nodules. In still other cases a sheet 

 of sillimanite occupies either side of a narrow dike of the quartz- 

 muscovite rock, in contact with the inclosing schists. The silli- 

 manite has a very finely fibrous felted structure, and is white to pale 

 greenish in color with a silky luster. One of the most marked prop- 

 erties of the mineral is its extreme tenacity. Where sheets of the 

 sillimanite occur in contact with the schists in the bed of the stream 

 the remainder of the dike has been completely eroded away leaving 

 a sheet of the sillimanite exposed. This sillimanite is almost entirely 

 fresh, unaltered and unstained, and scarce abraded at all, although 

 in a position to receive all the wear from stones carried by the tor- 

 rential brook which is here a succession of waterfalls. The hardness 

 of the sillimanite is 5; specific gravity, 3.172-3.180. Under the 

 microscope the mineral is seen to be composed of curved and di- 

 vergent aggregates of minute fibers, individually colorless but in 

 mass yielding a brown color by dispersion probabl}'^ from submicro- 



» Emerson. B. K., Geol. of Mass. and Rhode Island, Bull.. U. S. Geol. Surv. No. 597. 



