fenner: babingtonite from passaic county 555 



Chemical and physical properties. Qualitative tests on small 

 portions of the mineral gave strong reactions for iron, manganese, 

 lime, and silica. Tests for alumina, titanium oxide, magnesia, 

 and alkalies gave no indication of the presence of these. 



Before the blowpipe the mineral fuses without difficulty to a 

 black, slightly magnetic globule. Babingtonite from Baveno, 

 Italy (Nat. Mus. No. 86,183) and from Norway (Nat. Mus. No. 

 78,559) gave the same test. 



There is a very perfect, nearly scaly cleavage, which gives a 

 mirror-like surface. By comparison with the National Museum 

 crystals from Italy and Norway this is seen to be the cleavage 

 parallel to the basal pinacoid c, when the crystal is set up in the 

 position which Dauber has chosen.^ 



In the prism zone the cleavage is of columnar or fibrous 

 appearance. 



In babingtonite crystals from Italy and Norway vertical 



^ striation of faces in the prism zone is prominent. In a rough 



crystal which was broken out of the aggregate in the New Jersey 



specimen the same appearance was very evident. ^Moreover, 



in the casts similar striations frequently appear. 



A determination of specific gravity on apparently unaltered 

 fragments picked out under a binocular, using Rohrbach's solu- 

 tion according to Merwin's method,' gave a density of 3.398 at 

 21°. 



The optical properties were found to be as follows: Greatest 

 index of refraction in sodium light (immersion method) = 1.74. 

 Birefringence, y — a = 0.032. Optical character biaxial and 

 positive. The axial angle, 2 V, is evidently large, the bar of 

 the interference figure being nearly straight. Hintze gives 2 y = 

 60°-65°. In the New Jersey mineral a rather larger angle is 

 suggested by the slight curvature of the bar, but babingtonite 

 from Buckland, ]\Iass. (Nat. Mus. No. 80,668), and from Norway 



^ Crystallographers differ in their choice of positions for setting up the crystals. 

 The position chosen by Dana and Hintze brings out the crystallographic similarity 

 to the monoclinic pyroxenes, but the dominant habit of growth of the crystals 

 is prismatic in the direction of Dauber's prism zone. (See article by C. Palache 

 and F. R. Fraprie in Proc. Amer. Acad. Arts and Sci., 38, 11 : 383-393. 1902). Dau- 

 ber's orientation is adopted in the present paper. 



3 H. E. Merwin, Am. J. Sci., (4) 32: 425-428. 1911. 



