This VERY interesting rockhound story was written by Don Kasper (thanks for letting me post it for all my readers!). He tells me he doesn’t belong to any rock clubs but does associate with the Culver City rock club now and then. Again thanks to Don for the post and looking to hearing more of his rockhounding trips in the future!
Colorado River and Western Arizona Outing Notes:
Had the opportunity to meet up with Tony and Friends with the Needles
rock club last weekend. I thought I would document some of the photos
Tony took and maybe add a few cents on identifications of what we
found. We spent some effort to assemble collections in the photos
list for others to compare to our identifications. First I would
offer a few definitions that I use when I rockhound in the Mojave.
They would be:
Opalite: Opalized volcanic tuff. Opalite can come in a variety of
colors and can be associated with common opal and agate. Common
colors are whites, tans, and browns. Often has a wet appearance when
freshly fractured. Can be dendritic, if so, it’s a fine, hard
dendritic pattern occurring within the rock that can take a polish.
This material is very hard, forming prominent ridges and outcrops in
the . This is not colored common opal, which is much
softer, fractures readily, and forms rolling hills upon weathering.
Pastelite: Pastel colored Chert occurring in volcanic tuff and in
decomposed volcanic tuff and ash, that is, in Bentonite clay. This is
a highly expansive clay that looks like popcorn when dry, being
readily crushed when you walk on it. Common colors of Pastelite are
whites, tans, greys, browns, and blacks. The prized colors are blues
and violets. Can be solid, banded, and brecciated in appearance. Can
be concentrically banded to look like Wonderstone.
Both of these materials occur in lava/ash contact zones, with the
Pastelite appearing to favor Bentonite soils that are associated with
faulting and geothermal activity. The classic site for this is the
Hector mine that has Pastelite in a Bentonite that is so expansive
they it Hectorite. It is so waxy when wet it is used as a lubricant.
Faulting there has caused large formations of Travertine and
Aragonite associated with water and geothermal activity along the
fault that bisects the mine. That geology photo set will be posted on
a future day, but for now, back to Needles…
Near Needles is the town of Oatman. This is a famous locale of
Fire Agate that is an opalized brown chalcedony. Pay a $15
fee, and you can dig all day in the Cuesta claims. The claims cover
We traveled to
the mines to dig with the Needles club last week. Here is a huge piece
of Fire Agate rough. It is one foot
in size, valued at $1000 by the mine owner. It takes hard digging to
break the rhyolite for seams of opal. I used my favorite BLM legal
demolition tool–the 5-foot pry bar for moving stones to 1200 lbs to
get at a 3-inch pocket with 1/2-inch opal sheets. Without that,
others got little except for roaming Tony who seemed to hike most of
the rough 100 acres of boulders and ravines for his pieces. You take
a Dremmel drill with itsy bitsy diamond heads to burnish off the top
white chalcedony crust to get to the fire, then stop and use
successively finer heads, then diamond paste with a tiny brush head to
polish the pieces. Compared to Fire Opal, this material is harder,
and won’t fade, but is darker, so takes brighter light to see it
After a day digging with our Needles companions and after finishing
off their brownies, we headed out ourselves to Burro Creek
In the rough, they look like dull black lumps of coal. They
occur throughout the area as they weather out of the volcanic ash soil.
This is the Saguaro cactus that covers the hills there.
This is deep
Desert. You learn not to brush the plants or pick up things
without gloves quickly. You come to understand that myth that getting
too close to a cactus causes it to fling at you from body heat. The
spines of some like to Cholla have little barbs that make pulling them
out harder. The spines of one went right though Tony’s mountain boots.
This photo shows the man and his Pastelite locale at Burro Creek.
Clearly this had some geothermal activity and possible faulting. The
place is full of Bentonite clay with Chert nodules, the interesting
ones being Pastelite. I made the comparison to the Hector mine
earlier because if you have, like me, seen both, then you understand
that the geology of both sites are quite similar. Nearby (to the
immediate north) are caramel colored agate beds with a lifetime supply
for those interested. The ground is carpeted with agate. This may be
the only place I know where you can casually pick up agates to 20
banded Pastelite in the rough.
appears to be the elusive
Blue Agate, and in a spot where we cannot find any chipped
rocks, i.e., a virgin locale. Go figure. is just so vast.
Note the tuff crust surrounding the agate and the porous carbonates
and limestones indicating clear solution flows that were probably
geothermal. The colors range from baby blue to violet. Got a bucket
each, and will go back for more I am sure.
shows a 5lb chunk of grape agate that came from the Blue
site. This would be the largest specimen I have found. The specimen
was twice as big till I broke it in half. Made a mental note to turn
over any rock I find in Burro Creek before breaking it in the future.
We made our way back to the Colorado River to dig the gravel
benches. These are Coprolites, i.e. , dino dung. Can you see why?
They are jasper, but the particular swirl patterns are unlike anything
found in nature. Some consider them to be Gastroliths, stones eaten
by the big lizards to aide digestion where the marl patterns are
created by stomach acids. Tony speculated how some of the dung (not
shown) got flattened. Well, you can guess what he thought.
This is a collection of fossil stones in the river gravels. One
is a fresh water oyster. Some are corrals. Some have shell imprints.
Some have fish vertebrae casts. The biggie in back is another
Coprolite that got stream worn.
If you have comments or comparisons, let me know.