TERTIARY BASIC DIKE ROCKS. 
95 
Analyses of vogesite. 
SiC>2.. 
AI2O3. 
Fe 2 0 3 . 
FeO.. 
MgO. 
CaO.. 
Na20. 
K 2 0.. 
HjO- 
H s O+ 
TiOj.. 
ZrC> 2 . 
CO s .. 
P 2 O 3 .. 
I. 
II. 
I. 
II. 
47.31 
45.15 
so 3 . 
0.05 
16.21 
15.39 
Cl. 
.05 
5.05 
2.76 
FeS 2 . 
. 12 
2.90 
5.64 
Cr 2 0 3 . 
Trace. 
3.08 
6.38 
MnO. 
Trace. 
.14 
7.11 
8.83 
BaO. 
. 17 
3.92 
2.67 
SrO. 
.02 
3.73 
2. 77 
Li 2 0. 
Trace. 
Trace. 
87 
2.17 
2.85 
100.29 
100.21 
1.64 
2.80 
Less O for Cl. 
.01 
.01 
100.28 
4.98 
4.27 
.90 
.56 
I. Vogesite, Jennie Sample mine, Cripple Creek. W. T. Schaller, analyst. 
II. Vogesite, Castle Mountain. Bull. U. S. Geol. Survey No. 134, page 112. 
MONCHIQUITE. 
The monchiquites vary in granularity from aphanites to fine-grained por¬ 
phyries holding phenocrysts of dark pyroxene'", red olivine, and white amygdule- 
like grains of analcite. One specimen from a dike in the Gold Sovereign mine, has 
numerous flakes of dark biotite. Dikes referable to this group are known in many 
places, as in the Mollie Kathleen, Pointer, Gold Sovereign, Vindicator, Block 8, 
Ajax, Granite, Portland, and Strong mines, and in the Ophelia and Raven tunnels. 
A decomposed rock in the Ida May mine probably belongs here. 
The characteristic of this group is the presence of abundant phenocrysts of 
pyroxene and olivine embedded in a matrix of analcite. Orthoclase is not uncom¬ 
mon as small grains in the groundmass, and albite occurs sparingly in a similar 
manner. Analcite occurs in round grains of a millimeter or two in size, penetrated 
by and inclosing crystalline grains of pyroxene. It often shows the characteristic cubic 
cleavage and faint shadowy birefringence. In a few instances these areas of analcite 
contain minute crystalline grains of a clear and colorless mineral of slightly higher 
refractive index than analcite and a double refraction of about 0.001 or 0.002. 
They appear to be made up of several hexagonal plates partially merged. It seems 
possible that the mineral is a zeolite, and if so it may be gmelinite, with which it 
corresponds closely. That it is leucite is remotely possible. Analcite also occurs 
very evenly distributed throughout the rock as a matrix for the other constituents, 
but relative to the amount of pyroxene and olivine it is not abundant. In this 
mode of occurrence it resembles the material in the larger areas, being clear and 
colorless, of so low index that the surface appears rough, and occasionally showing 
faint polarization. In both cases the material is easily decomposed to a some¬ 
what turbid mineral, mostly developed in slender laths, which has properties 
corresponding to stilbite. Owing to the readiness with which analcite is dissolved, 
it is frequently partially replaced by dolomite. The pyroxene is probably augite 
and occurs in phenocrysts of two generations. The older individuals vary from 
