Washington — Kaersutite from Linosa and Greenland. 187 



Art. XXIII. — On Kaersutite from Linosa and Greenland ; 

 by Henry S. Washington ; with Optical Studies by 

 Fred. Eugene Wright. 



Introductory Note. — While visiting the small island of 

 Linosa, off the coast of Tunis, for the Carnegie Institution in 

 the summer of 1905, I found small crystals of a black amphi- 

 bole, accompanied by others of a glassy white, cleavable min- 

 eral, apparently a feldspar,* among the lapilli of a small, 

 parasitic cone of Monte Rosso. f The presence of amphibole 

 crystals here had previously been noted by Speciale4 Similar 

 crystals were also said to be found near I Faraglioni, but this 

 locality was not visited. Apart from these occurrences, am- 

 phibole is quite unknown in the lavas of Linosa, but the peculiar, 

 triclinic aenigmatite (cossyrite) is met with, though not abun- 

 dantly, and a kaersntite-like hornblende as well, in the lavas of 

 the near-by island of Pantelleria. 



Chemical analysis showed that the Linosa hornblende is very 

 high in titanium, and that in this, as well as in other respects, 

 it closely resembles the kaersutite of Greenland, which was 

 partially described in 1884 by Lorenzen.§ A comparative 

 investigation of the two minerals was therefore determined on, 

 the chemical work being done by me and the optical determi- 

 nations being very kindly undertaken by Dr. Wright, to whom 

 I am deeply indebted for his valuable and hearty collaboration. 

 Through the kindness of Professor X. V. Ussing, of Copen- 

 hagen, we obtained a piece of one of the best of Lorenzen's 

 original specimens of kaersutite, and we take this opportunity 

 to express our sincere thanks to him for his courtesy and great 

 liberality, without the aid of which the comparison would have 

 been sadly incomplete. 



The Linosa Amphibole. 



Physical Characters. — The Linosa amphibole is monoclinic 

 in crystal system and prismatic in habit. It occurs in roughly 

 developed crystals and fragments from 5 to 20 mm long by 3 

 to 8 mm thick, and bounded by the faces of the unit prism m 

 (110) and the clinopinacoid b (010). Terminal endings are usu- 

 ally^ absent, but a few of the crystals show the common forms 

 p (101) and r (011), which, however, were too imperfect to 

 admit of accurate measurement with the goniometer. Cleavage 

 parallel to m (110) is highly perfect, giving an angle of 55° 22' 



* A description of this mineral will be given in a separate paper, 

 f H. S. Washington, Jour. Geol., vol. xvi, p. 10, 1908. 

 % S. Speciale, Boll. Com. Geol. Ital., vol. xv, p. 2, 1884. 

 § J. Lorenzen, Medd. Gronl., vii, p. 27, 1884. 



