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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

 

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