MINERALS FROM LYON MOUNTAIN, CLINTON COUNTY 6l 



Type IV. Figures gsi-gh show a combination resulting from 

 the development of the negative rhombohedron A (0443) which 

 here replaces the planes of the pyramids y and T to the extent of 

 giving to crystals of this phase a rhombohedral aspect. The 

 pyramids y (8.8.16.3) and r (2243) which connect this combina- 

 tion with type III are present as faces of great brilliancy, as are 

 also the planes of v (2 131). The rhombohedron A (0443) here 

 replaces Y as a series of brilliant planes which yield excellent 

 reflections. Genetically this type corresponds closely with type 

 III, the crystals occurring with considerable secondary quartz 

 embedded in chlorite also of the second generation. The crystals 

 are clear and faintly yellow in color and measure from 6 to 

 10 mm on the vertical axis. 



. A curious variation of this type was noted on a large mass of 

 hornblende which was thickly incrusted with albite crystals.^ 

 These calcite crystals were symmetrically disposed in parallel 

 position on the six basal angles of a positive rhombohedron r 

 (loii) the latter evidently of a previous growth and considerably 

 ■etched and roughened on the surface. One of these composite 

 crystals is shown in figures lob-ioc and an enlargement of one of 

 the superposed secondary crystals in figure loa. The secondary 

 -crystals of this phase bear a general resemblance to the modified 

 combination of type III [figures 8 a- 8b] in that they show the scaleno- 

 hedronll: (14. 12. 26. 5) beveling the alternate polar edges of the 

 prevailing pyramid y (8.8.16.3). The pyramid -n- (1123) in the 

 same series with those previously noted appears as a terminal 

 modification consisting of deeply striated faces. The scaleno- 

 hedron /x, (5491) of type I here reappears for the first time as a 

 series of small but brilliant faces. The negative scalenohedron q : 

 (2461) characteristic of type II is he re represented by small brilliant 

 faces; from both of these latter forms, excellent reflections were 

 obtained. These two pyramids T (2243) and y (8.8.16.3) are 

 developed as large faces, the former giving fair reflections from 

 somewhat dull surfaces, and the latter bright and sharp reflections. 

 The three pyramids lie well in zone and agree closely as to measured 

 and calculated angles. The composite crystals as shown in figures 

 lob-ioc vary in size from 4 mm to 30 mm in diameter measured on 

 a basal axis. The superposed crystals frequently unite to form a 

 band encircling the primitive rhombohedron which latter in many 

 instances shows incipient forms of this habit irregularly disposed 



iThe writer is indebted to Mr H. H. Hindshaw for the loan of this handsome specimen as well 

 -as for material taken from it for study. 



