Washington — Kaersutite from Linosa and Greenland. 193 



undoubtedly the same as that mentioned by Phalen* in his 

 description of the rocks of the Nugsuaks Peninsula, who 

 speaks of it as forming a cliff 200 feet high, calls it picrite, and 

 gives a petrographic description. The kaersutite-bearing vein 

 is not mentioned by him. 



The specimens sent us by Professor Ussing show a rather 

 coarsely granular mass of feldspars pierced in all directions by 

 prisms of the black hornblende, which run up to 3 cm in length 

 by 5 mm in thickness. The rock is far from fresh, and is stained 

 brown and yellow with iron, and here and there a pale green. 

 Small grains of magnetite or ilmenite and many apatite crys- 

 tals in water-clear prisms 5 mra in length are present, and a few 

 small specks of pyrite were seen, but we could not detect with 

 certainty any of the mica megascopically. 



In thin section the texture is distinctly that of a granitoid 

 rock rather than that of vein material. The structure is decid- 

 edly miarolitic. The most abundant mineral is a plagioclase, 

 in anhedral development, whose extinction angles indicate the 

 average composition Ab a An 2 . (Extinction angle on 001 = 13°; 

 7 about 1"570 and a slightly > 1*56.) With this is some 

 alkali-feldspar, which shows some microperthitic features and 

 is apparently highly sodic, though it is mostly cloudy and con- 

 siderably decomposed. The brown kaersutite prisms are promi- 

 nent, and show the optical properties to be described later. 

 Small stout prisms of fresh augite are not uncommon. For 

 the most part they are colorless in the interior and slightly 

 greenish toward the border, but there are also some small anhe- 

 dra of a highly pleochroic, brilliant grass-green augite which 

 occasionally forms a border about the less colored variety, and 

 is apparently the chromiferous augite mentioned by Ussing. f 

 Indications only of the violet augite described by Ussing were 

 observed by us. 



Small thin plates of light brown biotite occur. These are 

 intensely pleochroic, the color for rays vibrating parallel to the 

 cleavage cracks being a very deep purplish red, while perpen- 

 dicular to this they are pale yellowish brown. They show no 

 analogy with astrophyllite. Some small grains of opaque ore 

 are present, but these only rarely occur as inclusions in the 

 hornblende and no pyrite was visible in our sections. Deep 

 red goethite was observed as an alteration product of the mag- 

 netite or pyrite. Apatite is very abundant, in long, clear 

 prisms, and is a frequent inclusion in the hornblende. It was 

 also noted by Ussing as an abundant constituent. Patches of 

 greenish chlorite minerals occur and are the cause of the occa- 

 sional green color of the rock. 



*W. C. Phalen. Smithson. Misc. Coll., vol. xlv, p. 194, 1904. 

 fin Eosenbusch, Mikr. Phys., vol. i, pt. 2, p. 237, 1905. 



