44 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
is another important component and proves to be a sodic oligoclase. Beside the 
prevailing albite twinning lamellae arranged according to the pericline law are 
sometimes seen. The mineral is often turbid through kaolinization. Orthoelase 
is more variable in amount, from fairly abundant to rare, but is on the whole less 
common than plagioclase. Microperthite is plentiful in some specimens, while less 
regular intergrowths, resulting in uneven extinction, are occasionally found. 
Quartz, though present in varying amount, is exceeded in abundance only by 
microcline when the group as a whole is considered. It occurs in irregular grains, 
ranging in size from exceedingly small ones up to those several millimeters in 
diameter. It is not much cracked, gives simultaneous extinction, and is glassy, 
but contains countless small fluid inclusions arranged in intersecting lines or planes 
which appear to have no definite crystallographic direction, or are crowded in 
certain parts. Another class of inclusions consists of minute hair-like rods or 
needles, without definite arrangement and usually of dark color. A few of the 
largest are brown and very strongly refracting, and it is possible that they are all 
composed of rutile. Several small rounded grains of quartz with the same orien¬ 
tation are sometimes seen penetrating an individual of feldspar, and more typical 
micropegmatitic intergrowths occur as small patches giving arborescent figures in 
polarized light; sometimes the orientation of one of the constituents is similar to 
that of a near-by individual of the same mineral. A decrease in the amount of 
quartz may produce a syenitic facies of the granite, like that from the Ajax mine, 
an analysis of which is given on the next page. 
Biotite is the only ferromagnesian mineral present and is rarely abundant. 
It occurs in isolated plates or as clusters of irregular scales and is usually greenish 
brown in basal sections and yellowish parallel to the vertical axis. Chloritization 
is sometimes considerably advanced, producing a material ranging from strongly 
pleochroic to almost colorless. Locally, along with the chlorite, small granular 
particles of epidote and of black iron ore separate out along cleavage planes. The 
colored chlorite apparently contains much of the iron of the mica, for separation 
of iron oxide is a less common accompaniment of the green than of the colorless 
variety. 
Of the accessory minerals, apatite in the usual prismatic habit and magnetite 
in large and small grains are the most common. Zircon is at times comparatively 
abundant. In numerous instances it is dull and in reflected light appears whitish 
and opaque as if through decomposition. Here and there a fragment of titanite 
is present . Some of the small brownish crystalline particles included in the quartz 
appear to be referable to rutile, while prismatic or rounded grains of a different 
character of brown, noticeably pleochroic, correspond to allanite. Minute corroded 
fragments of biotite when cut somewhat inclined to the base are readily confused 
with the latter mineral. Flakes of hematite or limonite, probably secondary, are 
sometimes present in the quartz and feldspar. Near mineral-bearing fissures 
pyrite and occasionally fluorite and zinc blende are introduced and the feldspars 
are partially sericitized. 
With the exception of the gneissic structure sometimes developed as above 
mentioned, the texture of these rocks is typically granular. 
