33Q 



University of California. 



[Vol. 2. 



axis. Hence the orientation of the axis of least elasticity must be 

 C:c=l4°34'.' 



In the absence of terminal planes it is impossible to determine 

 whether c divides the acute or obtuse angle between a and c. 



The indices of refraction of the different rays could not be 

 determined satisfactorily, owing to the nature of the material. 

 Approximate results were obtained by the method of Due de 

 Chaulnes, the figures being for a 1.6267, for y 1.6529, giving .0262 

 as the strength of double refraction. Compared with measurements 

 of a and y on Zillerthal actinolite by Levy and Le Croix* these 

 results are high, though the strength of double refraction is about 

 the same. 



Pleochroism is pronounced. The color of the c ray is bluish 

 green, of J) a lighter shade of green, and of b a yellow-green. 



The absorption formula is c>6>b. Sections parallel to the ver- 

 tical zone sometimes show unequal absorption. A similar phe- 

 nomenon was noted by Palachef in crossite, and by Daly J in 

 philipstadite. 



Cohesional Properties. — The study of the cohesional properties 

 of minerals has been applied to the members of the hornblende 

 series with marked success by Daly.|[ The material under consid- 

 eration yielded only prismatic planes, which were of sufficient 

 dimensions to admit of a satisfactory application of this method. 

 Also the microscopic cracks previously noted rendered it difficult 

 to obtain crystals which did not give rise to abnormal results, since 

 solvent action took place along these planes with great rapidity. 

 The crystals, or cleavage flakes, were etched with strong hydro- 

 fluoric acid at the temperature of boiling water for periods varying 

 from one to five minutes. Examination of the pits thus produced 

 was made with transmitted light, using a magnification of about 

 two hundred diameters. Essentially the same results were obtained 

 from crystals as from cleavage flakes, and no differences were 

 observed in the behavior of the actinolite from the two localities. 



* Comptes Rendu, Tome 106, p. 777. 

 tThis Bulletin, vol. i,p. 190. 



% Proc. Am. Acad. Arts and Sciences, vol. 34, p. 434. 

 || Proc. Am. Acad. Arts and Sciences, vol. 34, p. 374. 



