MINERALS FROM LYON MOUNTAIN, CLINTON COUNTY 6/ 



bole (hornblende) and always in close association with magnetite. 

 Several crystals were obtained which measured 5 to 15 mm in 

 diameter on the basal axes and 10 to 25 mm in vertical length. 

 These were of a decided prismatic habit, elongated parallel to the 

 c axis and showed, in the prismatic zone, a considerable develop- 

 ment of the planes of the unit prism. The ortho, clino and basal 

 pinacoids are present, the two former as narrow planes of medium 

 brilliancy and the latter as a series of broad but dull and rough 

 faces. The clinodome e (on) is also represented by a series of 

 rough faces, from which, however, fair readings were obtained by 

 using the method of a cemented cover glass. Well developed 

 planes of the positive hemipyramid i (211) were noted on two of 

 the largest crystals. Figures i5a-i5b show a combination of this 

 habit. 



Natural etch figures were noted in the prismatic zone on pris- 

 matic and pinacoidal faces. Their arrangement, shape and rela- 

 tions to adjacent edges are shown in figure 16. On the planes of 

 the clinopinacoid, these etch figures for the most part take the 

 form of elongated rhombs, the long edges of which are parallel to 

 the edges of the zone and the short edges of which are inclined 

 toward the intersection 010: on making the acute angles of the 

 rhombs 46°. In several instances a larger and shallower etch pit 

 was noted on these planes having its sides parallel to the pinacoidal 

 edges. Deep natural etchings occur on the faces of the ortho- 

 pinacoid, the etch pits in general conforming to the symmetry 

 required by the system. Two types of unsymmetric etch pits 

 shown at b and c on the middle section of figure 16 are apparent 

 exceptions to this general rule ; it will, however, be readily seen 

 that a combination of these two outlines produces a symmetric 

 figure of the outline shown at a. Two types of etch pits occurring 

 on the planes of the unit prism are shown at d and e. Both of 

 these types are triangular in shape and are oriented with the long 

 edges at an angle of about 8° with the zonal edges, as shown in the 

 figure. The curved edges in both instances point away from the 

 orthopinacoid and of the remaining straight edges those of type d 

 lie parallel to the intersection no: 001 and those of type e point 

 toward the negative quadrants, the angles with the zonal edges 

 being as indicated in figure 16. The etch figures show a marked 

 tendency toward arrangement in lines along these latter edges, in 

 the case of d these hnes lying parallel to the plane of parting which 

 may be assumed to have a direct influence on the shape of the 

 triangles of type d. 



