216 J. - S. Diller — Mineralogical Notes. 



mined with certainty. It seemed, however, as if the basal 

 plane in combination with the dia.ce showed positive electricity, 

 the same as the flat basal plane of the Mt. Antero crystals, 

 while the other basal plane showed negative electricity. 



In closing, I wish to express my thanks to Messrs. George 

 F. Kunz and C. S. Bement, who provided me with material 

 for study and to Mr, George L. English of Philadelphia, who 

 sent me a large number of Mt. Antero crystals for examina- 

 tion. 



Mineralogical Laboratory, Sheffield Scientific School, Dec. 12, 1888. 



Aet. XXVI. — Mineralogical Notes ; by J. S. Diller. 



1. Dumortierite from Harlem, N. Y., and Clip, Arizona '• by 

 J. S. Diller and J. E. Whitfield. 



IrT this Journal for Nov., 1887, p. 406, Dr. E. B. Eiggs pub- 

 lished a description, including a chemical analysis, of " The so- 

 called Harlem Indicolite," which was regarded as probably a 

 new boro-silicate. The notice led to correspondence with 

 Prof. E. S. Dana, who identified the mineral as dumortierite 

 and kindly sent us some of the original dumortierite from 

 near Lyons, France, for comparison. 



The physical properties of the Harlem dumortierite agree 

 very closely with those mentioned by Bertrand,* Gonnardf 

 and Damour4 Crystals are very rare. An imperfect one§ has 

 been observed with a( ooPoo ) and m{ o>P) equally developed. 

 Both planes are striated parallel to the vertical axis. Indis- 

 tinct reflections allowed only approximate measurement am— 

 152°, and therefore m??i=12i°. Obtuse terminal planes rarely 

 observed on embedded crystals. 



Cleavage parallel to a is distinctly developed so that when 

 the mineral is crushed and examined under a microscope cleav- 

 age plates may be found which show an obtuse bisectrix lying 



parallel to o{ ooPoo ). Cross fractures occasionally yield basal 

 sections which may be made to exhibit an acute bisectrix. Ex- 

 tinction always takes place parallel to the vertical axis and the 



*Bull. Soc. Min. d. France, vol. iii, p. 171, 1880, and vol. iv, p. 9, 1881. 



f Bull. Soc. Min. d. France, vol. iii, p. 2, 1881. 



% Bull. Soc. Min. d. France, vol. iv, p. 6, 1881. 



§ It was kindly loaned to us by Mr. R. T. Chamberlin of New York. Our 

 thanks are also due to Mr. Geo. F. Kunz for the material he so generously fur- 

 nished lor this investigation. It was collected along Fourth Avenue at 120th and 

 122nd Streets as well as near Ft. George, a new locality of the same district. 



