44 The American Geologist. •^"'^■' '^^■*- 
ing forms predominate, althoufi^h the orthodome and prism and 
pinacoids are frequently found ; the former measure up to 
35 mm., the single crystals up to 15 mm. Fan-like radi- 
ations incrusting the rock are quite common . 
Colors: milky white, gray, yellow, salmon, red-b^'own and 
brown 
Analyses, a, yellow; b. red-brown; c. grayish-'\hite ; d, 
flat radiations on granite from ^IcKinnon's quarry, German- 
town, Pa. 
a 
b 
c 
d. 
G. 
2.209 
57.00 
57-40 
2.197 
Si02 
58.53 
55-10 
ALO:, 
15.84 
14-97 
16.95 
14.18 
Fei'Oo 
2.08 
CaO 
8.02 
8.00 
9.40 
Na20 
.63 
• 54 
2.70 
K2O 
i.6s 
.40 
H.O 
14.67 
16.69 
16.87 
18.60 
99.34 99.76 100.7.8 
Natrolite : Less common than stilbite, occurring in most 
beautiful snow-white radiating acicular crystals up to 15 mm. 
in length; base almost invariably of white calcite. An anal- 
ysis afforded : 
G. 2 . 228 
Si02 47-80 
AI2O3 27.19 
CaO 1.50 
Na20 11.62 
K=0 1.68 
H2O 9-99 
narrow seams 
99-78 
Prehnite: 
Generally 
occurs 
massive in 
crystals rather 
rare; 
color 
Nile 
o- 
t5 
reen : 
Analysis of 
prehnite. 
G. 
2.952 
SiOi 
43-25 
AUO3 
20.29 
Fe.Oa 
4.87 
CaO 
26.76 
Na.O 
.59 
H2O 
4-38 
100. 14 
