214 THE CRYSTAL FALLS IKON-BEARING DISTRICT. 



The anijiliibole is in small needles. It has a very faint greenish tinge. 

 In cross section it shows marked prismatic development. The character of 

 the needles is pins in the long direction. The maximum angle found 

 between c : c is 18 degrees. The needles appear to be tremolite containing 

 some iron, and thus approaching actinolite in composition. Usually the 

 needles have no regular arrangement, l^ut in some of the pseudomorphs 

 with rectangular outlines there is a parallel arrangement of such a number 

 of the needles parallel to the long axis of the pseudomorphs as to give to 

 the pseudomorph a distinctly uniform polarization effect. 



Isolated crystals of magnetite and brownish transparent plates of 

 ilmenite are scattered among the actinolite needles. By far the greater part 

 of the iron oxide is collected in aggregates of small crystals and irregular 

 grains. The forination and aiTangement of these aggregates has in some 

 cases taken place along fracture and cleavage planes of the original minerals, 

 and thus in the pseudomorphs we see the mesh structure of olivine and 

 transverse parting of pyroxene clearly brought out. In other cases the iron 

 oxide is in irregular masses collected at the center or outlining the periphery 

 of the pseudomorphs or scattered in small masses through them. 



Between the tremolite needles and the iron oxide is a small quantity 

 of minute fibers. They have a greenish, tinge and low double refraction. 

 Their extinction is parallel to the long c axis, which is also the axis of least 

 elasticity. They are believed to be serpentine fibers. No definite arrange- 

 ment of these fibers could be discerned over the greater part of the pseudo- 

 morphs, but in one crystal, on the edge of the section, where it is especially 

 thin, the arrangement of these needles perpendicular to the long direction 

 of the iron aggregates outlining the meshes is unmistakable. Calcite is in 

 considerable quantity in some of the pseudomorphs. It is highly probable 

 that it owes its origin to the alteration of the original mineral, though some 

 of the calcium went into the amphibole. 



Besides the above-described pseudomorphs after olivine and pyroxene, 

 a few large prismatic and irregularly bounded areas were found among the 

 phenocrysts, which now consist chiefly of chlorite, with grains of calcite, 

 titanite, magnetite, and minute plates of ilmenite scattered tloi'ough them. 

 It is clear that the chlorite is derived from a hornblende, as shown by the 

 presence of ragged remnants of hornblende which possesses uniform orien- 

 tation throughout each area. This hornblende shows weak pleochroism in 



