42 
PENNSYLVANIA ANORTHOSITES 
is recognizable, but a few wedge-shaped crystals which are altered 
to zoisite probably represent this mineral. 
The results of a chemical analysis of a specimen near Forrest 
are given below. The chemical analysis of typical Adirondack 
anorthosite, from Mt. Marcy, is given for comparison. 
Honeybrook Anorthosite Adirondack Anorthosite 
W. T. Schaller, analyst, A. R. Leeds, analyst 
Si02 
52.86 
Quartz 
.54 
Si02 
54.47 
Quartz 
1.92 
AhOs 
26.68 
Orthoclase 
5.56 
AI2O3 
26.45 
Orthoclase 
5.56 
Fe 203 
1.03 
Albite 
37.73 
FezOa 
1.30 
Albite 
37.20 
FeO 
.74 
Anorthite 
50.04 
FeO 
.67 
Anorthite 
49.76 
MgO 
.38 
Diopside 
1.94 
MgO 
.69 
Diopside 
3.06 
CaO 
10.93 
Hypers thene 
.23 
CaO 
10.80 
Hypersthene 
.40 
Na20 
4.44 
Magnetite 
1.39 
NaaO 
4.37 
Magnetite 
1.86 
K 2 O 
.92 
Ilmenite 
.46 
K 2 O 
.92 
H 2 O 
.53 
H 2 O-I- 
1.49 
Apatite 
.67 
HaO-f 
.53 
H 2 O— 
.11 
H 2 O+ 
1.60 
100.29 
Ti02 
.25 
BaO 
.10 
100.20 
P2O3 
.33 
S 
— 
MnO 
.92 
MnO 
S 
.05 
■■ ■ 
BaO 
.03 
100.26 
CO 2 trace 
ZrOs trace 
100.26 
1 *5 ’"4 • (4) 5 ‘grano-labradorose. 1 *5 *4 * (4) 5 'grano-labradorose. 
The Honeybrook anorthosite falls into Class I, order 5, rang 4 (ap¬ 
proaching rang 3) and subrang 5 (transitional to sub rang 4) of the quan¬ 
titative system of classification, and as its mode is normative, the name 
becomes grano-labradorose. 
The Adirondack anorthosite falls into Class I, order 5, rang 4, and sub¬ 
rang 5 (transitional to subrang 4). The name becomes grano-labradorose. 
The border facies of the anorthosite*is less purely a feldspathic 
type of anorthosite. It is medium- to coarse-grained, light gray 
in color, streaked with irregular bands of mafic constituents. 
Occasional light green and gray areas indicate the presence of 
sericite and zoisite. In some localities the rock has a pseudo- 
porphyritic texture which is produced by the wavy arrangement 
of the dark bands about what appear to be large, single feldspar 
crystals. On close examination, however, the light areas are 
found to be composed not of single phenocrysts, but of many small 
interlocking crystals of feldspar. A few feldspar crystals meas¬ 
ure from one to almost three centimeters on their longer axis, but 
the average size of both the light and dark constituents is less 
than half a centimeter. 
