58 facets on a brilliant, the iargest stone has 77 facets and the second 66 facets, which add greatly to the beauty of the gems.
Origin of diamonds.—In
a paper read before the Geological Society of South Africa" F. W. Voit
discusses the nature and origin of kimberlite and its relation to the
diamonds found with it in South Africa. Doctor Voit prefers to call
kimberlite an agglomerate rather than a breccia. From the abundance of
pyroxene and other minerals besides olivine and a suspicion of the
presence of feldspar in some cases, the rock is evidently not a
peridotite, but might more appropriately be called porphyritic
pyroxenite. In places it is difficult to determine whether a rock is
kimberlite or diabase, and chemically there is a transition from the
one to the other. In many places diamonds are found where it would be
difficult to explain their presence otherwise than as having weathered
out of the diabase beds forming the surface rocks on some of the
plateau regions. The so-called bowlders of eclogite found at some of
the mines described by Doctor Bonney can very readily be explained as
segregations in the magma or as inclusions with edges and corners
dissolved off by the action of the kimberlite magma. The brecciation
evident in portions of the kimberlite bodies could readily have taken
place during the extensive serpentinization the latter have undergone
with consequent large increase of volume by hydration. The same agency
may have caused the breaking of some of the diamonds, though this
phenomenon is also readily explained in other ways.
EPIDOTE.
J.
D. Endicott, of Canon City, Colo., has had a quantity of compact
epidote cut "en cabochon" with pleasing results, for use in scarf pins,
cuff buttons, etc. This epidote is found in the unconsolidated drift
material 2 miles south of Canon City. The drift has been deposited in
terraces and beds over former table-lands and slopes south of Arkansas
River. The epidote is found as pebbles associated with cobbles and
pebbles of granite, quartz porphyry, trap, pegmatite, cyanite rock,
jasper, chert, iron ores, chalcedony, quartz, etc. Pebbles of granite
and diorite have a similar variety of epidote in streaks and irregular
patches through them, indicating the probable source of the gem
material. Only the very fine-grained compact variety of epidote
furnishes good gems. The greater part is too coarse-grained and brittle
for cutting. The colors range from light pistache or yellowish green to
dark olive-green. Occasionally a bright-red patch of jasper is included
in the epidote, giving somewhat the effect of bloodstone. The epidote
is hard, and if sufficiently compact takes a beautiful polish. It has
found favor in the local markets in Colorado and should be received
elsewhere.
FELDSPAR GEMS—AMAZON STONE, MOONSTONE, ETC.
COLORADO.
The
Pikes Peak region has long been famous as a source of beautiful
crystals of amazon stone and associated smoky and clear quartz. One of
the most prolific areas has been that called Crystal Park by
collectors, lying from 2 to 4 miles southwest and south of Manitou
"Abstracted in Eng. and Min. Jour., April 17,1909.
