C. H. Warren — Mineralogical Notes. 341 



radiating fibers. Tliin sections from such portions show clearly 

 that the fayalite has been altered by mineralizing solutions 

 which gained access along crevices, cleavage cracks, or along 

 the lines of magnetite inclusions, evidently drawn in by the 

 force of capillary action. Every stage in the alteration of the 

 fayalite can be seen, from that of the pure iron silicate with 

 only now and then an encroaching liber of anthophyllite, 

 through those stages where patches or islands of fayalite are 

 entirely surrounded by the secondary fibers, to the stage where 

 the change is complete and the field is entirely composed of 

 anthophyllite with grains of residual magnetite. The mag- 

 netite shows no evidence of having played a part in the reaction 

 other than to sei've as nuclei for the radiating groups of fibers. 



Under the microscope between crossed nicols, the fibers 

 show parallel extinction, a fairly high single and a high double 

 refraction. Cross sections of a group of fibers show that each 

 one is a minute prismatic crystal of an amphibole, the sides of 

 the prisms making angles that measured approximately 123 and 

 57 degrees. A careful study of prismatic and basal sections 

 was made in parallel polarized light with a quartz wedge in order 

 to determine the position of the different vibration directions. 

 The following relations were established ; c — a, ci^z^ 5=b, axial 

 plane parallel to the brachypinacoid. In convergent light a 

 biaxial interference figure is obtained from sections parallel to 

 the macropinacoid. The axial angle is large, the loci of the 

 hyperbolas lying just in the edge of the field of the microscope. 

 The character of the double refraction is positive and the dis- 

 persion is well marked, red less than violet. 



Basal sections are also confirmatory of the above since they 

 show the central portion of an obtuse interference figure. 



Before the blowpipe the fibers blacken, round slightly and 

 become strongly magnetic. They are insoluble in acids. Care- 

 ful qualitative tests show the mineral to be a practically pure iron 

 silicate, with only traces of aluminium and magnesium. It 

 seems, therefore, that the fibers are those of a pure iron antho- 

 phyllite, and represent a new member of the amphibole group. 

 The formation of this metasilicate of iron from the orthosili- 

 cate by the addition of SiO^ derived from the pegmatite, may 

 be illustrated by the following equation : 



Fe,SiO, + SiO,=Fe,Si„p,. 

 Fayalite Anthophyllite 



A quantitative analysis to verify the above conclusion is 

 desirable, and it is hoped that the time and facilities for mak- 

 ing it may soon be available. 



Intimately associated with the anthophyllite is a dark green 

 lepidomelane mica. It usually lies with its cleavage faces 



