S. L. Penfield — Anthophyllite from Franklin. _ZV. C. 395 



curved contours. They frequently show vertical striations, 

 especially that part of the prism which is nearest to the obtuse 

 angle, and this is frequently rounded off by the oscillatory 

 combination. Nine of the best selected crystals were measured 

 on the reflecting goniometer, but the reflections were somewhat 

 uncertain owing to the striations and surface markings on the 

 prismatic faces. The two best measurements were /a/, 

 110a 110 = 125° 37' and 125° 38', while the average of fifteen 

 measurements each of 



110 aIIO, varying from 125° 25' — 125° 41' = 125° 35' 

 110 a 110, varying from 54° 12'— 54° 34' = 54° 25' 



If we take therefore 125° 37' as the best measurement, it is 

 very close to the average given above and will certainly very 

 nearly represent the true value. From this the ratio d'.b = 

 •51375 : 1. The above values vary somewhat from the deter- 

 minations of Des Cloizeaux* on the anthophyllite from Kongs- 

 berg in Norway, who gives for 1^1 about 125°. 



The cleavage is very perfect parallel to the prism, 110, and 

 brachy-pinacoid, 010 ; the latter is easily produced and yields 

 brilliant surfaces although it is always mentioned in the min- 

 eralogies as indistinct. The cleavage parallel to the macro- 

 pinacoid, 100, which is always mentioned as perfect was poor 

 and scarcely perceptible. 



The crystals are very transparent and have a delicate clove- 

 brown color, the largest ones affording good material for deter- 

 mining the optical properties. The plane of the optical axes 

 is in the brachy-pinacoid, as in all anthophyllites. Two plates 

 were cut, one parallel to the macro pinacoid, the other parallel 

 to the base. The latter was small and considerable difficulty 

 was experienced in making it at right angles to the good 

 cleavages. From these two plates the divergence of the optical 

 axes was measured on a large axial angle apparatus in the 

 potassium mercuric iodide solution whose indices of refraction 

 were n, red, Li = 1*6650 ; n, yellow, !Na = 1*6811; n, green, 

 Tl = 1*7086 witli the following results : 



Macro-pinacoid section. Basal section. 

 2 H for red = 87° 31' 87° 24' 



2 H lor yellow = 85 45 88 5 



2 rl for green = 83 44 88 28 



irom which we can calculate : 



2 V red =90° 4' ■ (3 = 1*6276 



2 V yellow = 88 46 (3 = 1*6353 



2 V green = 87 28 /3 = 1-6495 



* Manuel de Mineralogie, i, p. 75. 



