Peridot in Colorado abstract from Rocky Mountain
Gemstone Symposium, Colorado School of Mines, Golden, Colorado,
September 7, 8, 9, & 10th, 2002
Peridot in Colorado
By John A. Rhoads
D&J Rare Gems, Ltd.
A small but significant deposit of gem grade peridot occurs
within the San Isabel
National Forest on the border of Fremont and Park counties in
the vicinity of the junction
of these two counties with Chaffee County. The map coordinates
are N 38 degrees 41.50
minutes, W 105 degrees 51.60 minutes at an elevation of approximately
9,580 feet. The
location can be found on the Cameron Mountain 15’ quadrangle
and 7.5” Gribbles Park
USGS topographic maps. Access to the area can be obtained by
taking Chaffee County
Road 175 just north of Salida, Colorado, into Fremont County
where it becomes Fremont
County Rd 2 and turning left at the Everett Cattle Camp on the
road to Herring Park and
Cable Gulch. A rough dirt road that branches off from this road
about two miles from the
junction leads to the top of the mesa. The flat top mesa with
the peridot bearing basalt
can be seen in the distance to the north approximately 2 miles
away from the junction.
The two mesas encompass an area of approximately 3 square miles
in a very irregular
shape. This areas has been known to produce gem grade peridot
for many years although
it has only been since the early 1990’s that it became common
knowledge to collectors.
The area appears to be covered by at least three separate episodes
of basalt extrusion
that occurred during the Tertiary Period. Capping the mesas is
a reddish, highly gaseous
basalt, known as scoria, that is barren of any included minerals.
In some areas the cavities
left by the gases are so numerous that even the largest boulders
can be lifted with ease.
Another episode of deposition of red basalt contains mostly black
hornblende xenocrysts.
Some of these inclusions are very rounded indicating some reabsorption
during the
migration of the magma. The peridot occurs in a gray, very solid
basalt almost completely
lacking in gas cavities. This basalt usually occurs beneath the
other two episodes of
deposition. This basalt is very tough and efforts to remove any
of the peridot it contains
usually results in fracturing of the peridot long before the
basalt breaks. Underlying the
basalt is a gray limestone, possibly the Leadville Formation
of Pennsylvanian age.
Small gem grade pieces of peridot are found weathering out of
the basalt that caps
two small mesas in this area. The upper flat areas of the mesa
are generally barren of
peridot with most occurring on the slopes below the top appearing
to weather out several
feet beneath the upper most layer. The best collecting areas
appear to occur where the
slope is gentle just below the weathering layer allowing for
the mineral grains to
accumulate rather than disperse down a steeper slope. Over a
dozen different locations on
the slopes surrounding the mesas have been found to contain gem
grade peridot although
some are more productive than others.
Peridot is also found within the basalt in knots (peridotite
xenoliths) up to 5
centimeter in diameter although these knots are highly fractured
and do not produce single
rough pieces of comparable size. Smaller, solid grains of peridot
under a carat in size are
predominate in some basalts while the highly fractured knots
occur in others.
A second location, known as the “Lone Pine” area which
is a small basalt knoll
located approximately 2 miles south of the two mesas and is easily
located and identified
about a mile east of the junction of Fremont County Rd 2 and
the Herring Park / Cable
Gulch Road on Fremont County Rd 2 by the lone pine tree that
grows on the
northwestern edge of the deposit. This deposit contains a mix
of both loose grains of peridot that have weathered out of the
basalt as well as those “frozen” in
the host rock.
The color of the peridot cut from the rough from this area is
a very fine, medium, lime
green. The color is fairly consistent throughout the deposit.
Finished gems are very bright
and popular among collectors for their fine color and luster.
Inclusions in the peridot are rare. Two gems cut from rough found
approximately a
mile apart contain during the 2002 collecting season contain
similar, high relief, rounded
crystals that so far have not been examined for identification.
Sizes of the rough and cut gems from these locations are small
compared to peridot
from other locations throughout the world. Most of the rough
grains of peridot are well
under a carat in size. Grains over a carat are fairly common
with those over 2 carats being
exceptional and any over three carats a major find. The largest
rough piece known
weighed 8.17 carats, however, the shape was very irregular and
the gem cut from this
piece of rough weighed only 1.54 carats. It is currently in the
Denver Museum of Nature
and Science collection. The largest recorded cut peridot from these
locations is a 2.87
carat gem Robert Spomer cut for a client. A cushion cut gem weighing
2.47 cts was cut
from a piece of rough weighing 5.44 carats by John Rhoads for
a client. This gem was
particularly clean of excellent quality. Another gem of 2.08
carats was cut from rough
found in the Fall of 2001 by John Rhoads and is currently in
the DMNS collection.
Numerous gems between 1 and 2 carats in size have been cut by
John Rhoads with
several of them currently in the DMNS collection. Rumors of recent
finds of rough as
large as 14 carats have gone unsubstantiated.
Other minerals that are found in association with the peridot
are black cleavage
fragments of amphibole group minerals. Gem grade fragments of
colorless quartz is found
with the loose peridot. Some light purple quartz (amethyst) has
been cut with a knot of
this material discovered intact in September of 2001. Also a
dark green mineral of gem
grade has been found in association with the peridot that tests
within the indices of
enstatite although verification of this identification has not
been established at the time of
writing this report. (The gem cut from this dark green minerals
has since been identified by GIA as "enstatite". December
2002)
Gem grade peridot has been reported from several other areas
in the vicinity of this
deposit but as of this writing none of them have been confirmed.
Current status of the area is pretty much open to collecting.
During the mid-1990’s
Robert Spomer and several associates filed the “Green Beebee”
claim on one of the more
productive areas to keep it open to collecting. A few years later
a group from Canon City,
Colorado, have filed claims to the north of the mesa and are
currently active according to
one of the owners. Please observe their claim markers if in the
area. These areas have
since been heavily collected by rockhounds. The best time for
collecting is immediately
after a storm or following the melting of snow that covers the
area during the winter. The
area is usually accessible to collecting from late April until
November. Caution should be
taken if collecting during hunting season as this is a very popular
area for deer, antelope,
elk, and bears.
If planning on visiting this area to collect respect any current
claims. Do not bury but
carry out all trash. Remain on current roads with vehicles as
flora in this area is very
fragile and takes years to recover from even a single off road
venture.
Should you visit the area and find an exceptional piece of rough
that results in a
superior finished gem both Jack Murphy and Pete Modreski as well
as myself would like
to hear about it.
Happy collecting!
John A. Rhoads
D&J Rare Gems, Ltd.
1 719 530 0628
Please visit our sister site D
and J Rare Gems.
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