340 C. II. Warren — Mineralogical Botes. 



It is the object of this paper to once more call attention to 

 the remarkable occurrence of this rare mineral, and to describe 

 an interesting zone of a new fibrous amphibole which has 

 resulted from the reaction between the silica of the enclosing 

 pegmatite and the fayalite. 



The fayalite of this second find appears to be identical in 

 character, and in its general mode of occurrence, with that 

 described by the authors cited above, although it was some- 

 what larger in size. The several large and fine specimens, 

 which the discoverers very kindly brought to the author for 

 examination, indicate clearly that the mass was roughly len- 

 ticular in form, having a maximum thickness of about ten 

 inches and tapering from this to an edge of about 0*5 inches. 

 Mr. Horton states that about 250 pounds was taken out in all, 

 and that it was entirely surrounded by the pegmatite, portions 

 of which still adhered to the specimens studied. The mineral 

 was for the most part fresh, showing, however, in some of the 

 thinner portions alteration to a brown ferruginous powder. 



Magnetite occurs chiefly as a marginal secretion. A narrow 

 granular rim never exceeding a few millimeters in width prac- 

 tically surrounds the fayalite, while single grains often attain- 

 ing a diameter of 4"'"' are often observed near the outside of 

 the mass. 



Thin sections examined under the microscope show that 

 magnetite is quite plentifully scattered through the fayalite in 

 the form of very minute grains, which have the characteristic 

 cross sections of magnetite. The grains are frequently arranged 

 in rows, which extend across the fayalite very much in the 

 way that inclusions do in the quartz of many rock sections. 



Where the fayalite comes in contact with the quartz of the 

 pegmatite, a reaction rim is developed consisting of radial 

 fibrous aggregates. The fibers shoot out into the fayalite on 

 one hand and into the quartz on the other. The line of sepa- 

 ration which marked the original contact is distinct, and 

 passes through the centers of the radial groups. The zone 

 varies in width from 3 to 8"'"", although in one instance, where 

 an overlapping of an edge of the fayalite had occurred, a mass 

 of fibrous mineral some 3^"" in thickness was observed. 



The fibers are translucent, white to a light brown in color, 

 and at once suggest anthophyllite by their appearance. On the 

 side toward the fayalite, magnetite grains are embedded in the 

 mass of fibers, which, as will appear later, are residual after 

 the alteration of the fayalite to anthophyllite. The mineral is 

 seen both in radiating groups and as isolated fibers in portions 

 of the fayalite near the margin, but none has been observed at 

 a greater distance than three or four centimeters from it. The 

 larger magnetite grains usually act as the center for a group of 



