Contrary to popular belief, _granite_ (crystalline igneous rock composed
principally of quartz and feldspar) forms only a part of the Teton
Range. The Grand Teton (fig. 6) and most surrounding subsidiary peaks
are sculptured from an irregular mass of granite exposed continuously
along the backbone of the range from Buck Mountain northward toward
upper Leigh Canyon. The rock is commonly fine grained, white or
light-gray, and is largely composed of crystals of gray quartz and white
feldspar about the size and texture of the grains in very coarse lump
sugar. Flakes of black or dark-brown mica (biotite) and silvery white
mica (_muscovite_) about the size of grains of pepper are scattered
through the rock.
From the floor of Jackson Hole the granite cliffs and buttresses of the
high peaks appear nearly white in contrast to the more somber grays and
browns of surrounding gneisses and schists. These dark rocks are laced
by a network of irregular light-colored granite dikes ranging in
thickness from fractions of an inch to tens of feet (fig. 23).
[Illustration: Figure 22. _Indian bowls carved from soapstone,
probably from the Teton Range. Mouth of the unbroken bowl is about 4
inches in diameter._]
The largest masses of granite contain abundant unoriented angular blocks
and slabs of the older gneisses. These inclusions range from a few
inches in diameter (fig. 24) to slabs hundreds of feet thick and
thousands of feet long.
Dikes or irregular intrusions of pegmatite are found in almost every
exposure of granite. _Pegmatite_ contains the same minerals as granite
but the individual mineral crystals are several inches or even as much
as a foot in diameter.
Some pegmatites contain silvery plates or tabular crystals of muscovite
mica as much as 6 inches across that can be split into transparent
sheets with a pocket knife. Others have dark-brown biotite mica in
crystals about the size and shape of the blade of a table knife.
A few pegmatites contain scattered red-brown crystals of garnet ranging
in size from that of a BB shot to a small marble; a few in Garnet Canyon
and Glacier Gulch are larger than baseballs (fig. 25). The garnets are
fractured and many are partly altered to _chlorite_ (a dull-green
micaceous mineral) so they are of no value as gems.