194 Washington — Kaersutite from Linosa and Greenland. 



A hornblende which apparently resembles that of Kaersut is 

 described by Phalen* as occurring in a fine-grained quartz- 

 monzonite at Alanekerdlak on the Nugsuaks Peninsula. From 

 our examination of the original specimen, kindly loaned by 

 Dr. G. P. Merrill of the Smithsonian Institution, it appears 

 that, while the rock resembles that of Kaersut, except in its 

 liner grain, this hornblende differs from ours, being of a yellow- 

 brown rather than a red-brown color, and with somewhat 

 different pleochroism. The optical characters were not deter- 

 mined, but it would appear to be titaniferous and related to 

 that which we are describing. 



Physical Properties. — The Kaersut amphibole is mono- 

 clinic and forms prisms which reach a length of 3 cm and thick- 

 ness of 5 min in our specimens. They are bounded by the prism 

 m (110) and the pinacoid b (010). The terminations are usually 

 poor, but some crystals show the presence of steep domes or 

 pyramids, whose symbols could not be determined. These are 

 ajso to be seen in the thin sections. Ussingf gives (110), (Oil), 

 (101), and more rarely (121) and (010), as the forms observed 

 by him. Twinning was observed in several of the sections. 

 In one case the twinning plane was probably a steep dome, 

 making an angle of 13° with the cleavage lines, and showing 

 in several places several narrow lamellae due to repeated twin- 

 ning. The cleavage lines cut this twinning trace uninterrupt- 

 edly. This crystal is shown in fig. 4, from a photograph 

 kindly made for us by Prof. J. Volney Lewis. The extinction 

 is parallel to the right of the twinning line and 17° to the 

 left. The crystals are seen in thin section to be frequently 

 crossed by narrow cracks (seen as dark lines in the figure). 

 Some of these are irregular, but many are straight and parallel, 

 crossing_the cleavage lines of 110 at about 32°. For the angle 

 110 /v 110 measured on the cleavage surfaces, Lorenzen (p. 29) 

 gives 55° 29' (the mean of 55° 25"' and 55° 33'), while Ussing 

 obtained 55° 35'. On an excellent cleavage piece, giving sharp 

 reflexion signals, Wright obtained 55° 35', while on less satis- 

 factory fragments the values were 55° 34' and 55° 23'. We 

 therefore consider that 55° 35' best represents the value. For 

 other angles Ussing gives the following: 101^011 = 34° 16 r , 

 101 ^ 110 = 76° 51' 110 ^ 011 = 68° 44'. The cleavage is 

 highly perfect, and where it is not developed the fracture is 

 conchoidal. We found the hardness to be about 6 ; Lorenzen 

 gives it as 5*5. The mineral is very brittle, and fuses readily 

 before the blowpipe to a dark, magnetic bead. 



The specific gravity as determined by Washington with the 

 pycno meter on about one gram of very carefully selected frag- 



*W. C. Phalen, loc. cit., p. 207. 



f N. V. Ussing, in Kosenbusch, Mikr. Phys., vol. i, pt. 2, p. 236, 1905. 



