1908 ] 
Micropegmatite at Chapel Hill 
105 
quartz is best seen in this relation in long, spindle-shaped forms 
with parallel orientiation over a considerable portion of the field. 
These are wholly inclosed in orthoclase or microcline and extin- 
guish simultaneously over wide areas. Measurements with a mi- 
crometer eye-piece gave lengths of .58 m.m., .62 m.m., and .69 
m.m. for the longer quartz spindles. In places the large spindles 
radiate from centers in which (dusters of smaller quartz crystals 
are imbedded in orthoclase and microcline. There are a few 
places where quartz occurs in the triangular and knee-shaped form 
characteristic of graphic granite as originally described. 
The orthoclase is very abundant and forms a large percentage of 
the rock. Crystal boundaiies are very indistinct. Large areas 
inclosing the quartz spindles extinguish as single crystals sepa- 
rately from the quartz. 
Microcline is less abundant than orthoclase, and the areas 
occupied are smaller. Crystal boundaries are indistinct. 
The impression first given by the slide is that the orthoclase and 
microcline were the last to crystallize, and constitute a groundmass 
in which the quartz is set, but a careful examination reveals many 
quartz-feldspar boundaries in which the two minerals are mutu- 
ally interpenetrating. Many quartzes also contain small poikilitic 
inclusions of orthoclase. It is therefore probable that the 
quartz and the alkali feldspars crystallized contemporaneously. 
University of North Carolina 
Chapel Hill, N. C. 
March 11, 1908 
