Palacki;. I 



New Soda Amphibole, 



Constituent Minerals. — The blue amphibole crystals lie with 

 their longest axes in the planes of schistosity, but further than this 

 are not in parallel orientation. They vary in size from the most 

 minute needles to columns 20 mm. or more in length and 3 mm. 

 in diameter; but, as a rule, most of the crystals appearing on any 

 given surface are of the same general dimensions, and decrease in 

 number as they increase in size. The friable character of the matrix 

 renders it easy to extract crystals of the amphibole, and such crys- 

 tals always exhibit more or less perfectly developed crystal outlines. 

 The forms observed were the prism, coP, and the clinopinacoid, 

 coPoo , the oscillatory combination of which generally produces 

 deeply striated or rounded faces. One crystal was, however, ob- 

 tained which afforded fairly good reflections in the goniometer, 

 and the angles shown in the accompanying diagram, Fig. 1, were 

 obtained from its measurement. No terminal planes were observed, 

 either macroscopically or microscopically. 



Under the microscope the matrix of the rock appears as a 

 homogeneous aggregate of allotriomorphic feldspar grains, very 

 uniform in size and perfectly fresh and water-clear. The grains 

 rarely exhibit any distinct cleavage. Twinning is also very rare, 

 and, when present, follows the albite law. Measurements of extinc- 

 tion angles on such twins give angles averaging 16 on M, indi- 

 cating that the feldspar is albite. The strong resemblance of much 



