MINERALS FROM LYON MOUNTAIN, CLINTON COUNTY 69 



(0 = 3.37) indicating a clearly marked hornblende. The extinc- 

 tion angle observed on a section cut parallel to oio gave c A C 

 30° 15'. Thin sections are highly pleochroic; a = yellowish green, 

 C =^ greenish blue. 



Thin sections of the wall rock show the derivation of hornblende 

 from the augite previously described, the former mineral therefore 

 taking rank as a secondary derivative. A subsequent change 

 corresponding in generation to the calcite crystals of types III, IV 

 and V has produced from the black hornblende a light green bysso- 

 lite which in its advanced stages of metamorphism is reduced 

 to a whitish, asbestic amphibole. A striking example of this 

 first change is shown in the specimen depicted in plate lo 

 where the black hornblende is seen to terminate in feathery 

 brushes of byssolite which latter mineral is accompanied by 

 secondary albite derived from the primary orthoclase. The 

 byssolite, in its color, properties and association resembles 

 that from Knappenwand in the Tyrol. As near as could be 

 determined the extinction angle measures c A C= 15°. 



Zircon 



Zircon is found in pegmatite in close proximity to the iron ore at 

 the Parkhurst shaft, i^ miles east of the main workings at Lyon 

 Mountain. The crystals which occur embedded in orthoclase and 

 quartz range in size from 8 to .5 mm in diameter, the larger indi- 

 viduals invariably occurring in orthoclase. They are lilac-brown 

 in color and vary in translucency from opaque in the larger speci- 

 mens to translucent in the smaller ones, many of which show 

 reddish by transmitted light. Many of the crystals show grayish 

 zones symmetrically disposed on the terminations as indicated in 

 figure i8b. The faces in the prismatic zone are sharp and brilliant 

 and gave excellent reflections. In the zone [iio.iii] the 

 planes of u and v are narrow and ill defined but, however, yield 

 fair reflections and were established beyond question. The dite- 

 tragonal pyramid a; (311) occurs only on the smaller crystals shown 

 in figures iga-iQb, which were found embedded in quartz. In 

 general these latter crystals were more brilliant and perfectly formed 

 and yielded better reflections than the larger types represented in 

 figures i8a-i8b. 



