Kansas is a state with abundant fossil and mineral
resources, but with few specimens that rockhounds would consider gemstones or
even semi-precious gemstones. However,
there are some very nice cabinet specimens available for most collectors. The problem usually associated with
collecting in Kansas is that virtually all land is privately owned and/or state
land is off-limits to collecting---so, ask permission before trespassing.
Minerals in the eastern part of the state were noted in the Blog Posting of
March 23, 2013.
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Generalized geologic map of Kansas. The eastern one third of the state has
bedrock of Mississippian, Pennsylvanian and Permian age (blues and purples).
Outcrops of Cretaceous rocks (green) and Cenozoic (yellow, tan and brown)
dominate in the western section. Map
from Kansas Geological Survey.
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The Cretaceous rocks cropping out in the center and
western part of the state offer numerous mineral collecting localities, many
more than the average rockhound is aware. Near, and at, Kanopolis Reservoir
(west of Salina but near I-70, Exit 238) are exposures of gray-black shales of
the Kiowa Formation. Unique specimens of
Turritella gastropods replaced by
pyrite/marcasite are scattered along the shoreline of the reservoir as are
nuggets of marcasite. In other
Cretaceous black shales the pyrite/marcasite is the fossilization agent in cephalopods
such as Scaphites (Blue Hill Shale)
and Baculites (Pierre Shale). In addition to the Kanopolis gastropods, strange
nests of fibrous calcite, cone-in-cone, occur in beds and lenses in the Kiowa
Formation. Rockhounds should explore exposures
along the dam face (if Corps of Engineers regulations allow such) as collecting
both cone-in-cone and Turritella is “easy”.
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Part of cone-in-cone structure
that has broken away from the main mass.
Note circular pattern on top surface.
From the Cretaceous Kiowa Formation.
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East of the Reservoir is the small community of
Bavaria (along KS 140) where “barite roses” (barite-cemented sand grains) have
been collected in road cuts from the Kiowa.
I have not found the “roses” in many decades (one remaining from a teenage excursion) ) and also have some small tabular crystals.
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Small
cluster of barite crystals collected from Kiowa Formation near Bavaria, Kansas.
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Amber is quite rare in Kansas, as elsewhere, but has
been reported from the Kiowa Formation at Kanopolis Reservoir (locality now
under water). A description and photos
of the amber may be located in Blog Posting September 23, 2012. Perhaps additional exploration would turn up
new localities?
In many exposures of the Cretaceous dark shales,
gypsum crystals (selenite) are scattered on the surface. The gypsum is secondary and may form from the
weathering of pyrite/marcasite, or enrichment by groundwater. Some of these crystals are from five to seven
inches in length and many are twinned.
Perhaps one of the easiest places to collect is from exposures of the
Dakota Formation (Cretaceous) in the overflow spillway at Wilson Reservoir
(Russell County, north of Exit 206, I-70).
Other Cretaceous black shales, especially the Blue
Hill Shale Member of the Carlile Shale, often contain concretions that collectors
term septarians. When I was teaching in
Kansas, numerous people showed up in my office lugging along their “fossil
turtles”. It was my duty to bust the balloon
and inform them their rock was a septarian concretion. I tried to encourage them to closely examine
the concretion and notice that the internal cracks in the concretions are secondarily
filled with calcite. They actually make
nice collectable specimens but nab a small one as some are larger than a
motorcycle! Rockhounds should consult a geologic map of
Kansas and pinpoint outcrops, especially around Cedar Bluff Reservoir south of
I-70 (Exit 135), and prospect. In
addition, some concretions in the Pierre Shale of Wallace County (far western
Kansas) contain crystals of barite; however, most of these specimens are
located on private land and inaccessible.
The limey portions in the Cretaceous rocks sometimes
contain beds and crystals of nice calcite.
The Smoky Hill Chalk Member of the Niobrara Formation often has joints
filled with secondary crystals. These seams
extend for tens of feet and produce some really great calcite specimens. Collectors might examine any Smoky Hill
exposure, especially in northern Ellis County (off I-70, Exit 145), and chances
are good for locating crystals.
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Calcite
crystals from seam in Smoky Hill Chalk, Ellis County.
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Silicified beds in the Neogene Ogallala
Formation/Group have been collected since the early part of the 20th century,
mainly from Kansas, but also in parts of Nebraska and Texas. The best known of
these silicified beds is the aptly named the “Green Quartzite”, a quartz- to
opal-cemented sandstone and/or conglomerate that forms the local ”caprock” in many western Kansas
localities. Of greater interest to
rockhounds are the concretions and beds described by Frye and Swineford (1946) as irregular
masses (up to 8 inches in long diameter) of dense, cream-colored,
waxy or resinous opal…containing vugs lined or filled with
the more common translucent opal and some chalcedony, and on the
outside consists of dull white porous silica… The rock is brittle and breaks
easily with pronounced conchoidal fracture into small splinters. The
current thought is that the source of silica was the vast beds of volcanic ash
scattered throughout the Ogallala. Essentially this opal is a weathering
product---silica leaching downward from the overlying ash beds.
The opalized nodules collected ~15 miles
south of Wallace, Kansas, are among the most beautiful of the opalized
concretions that I have observed. Some of the translucent opal is almost, or
may be, gem quality. Although small, “moss” dendrites (manganese oxide) are
also present. I am unaware of jewelry, cabochons
or faceted stones from Ogallala opal. But---there is always a first time!
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| The "moss opal" or "moss agate" from Gove County Kansas. This slice is more of a dendritic chalcedony and is not very "opalized." Width ~4.3 cm. |
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Opalized sandstone from Ogallala Formation,
Wallace County. Arrows point to "opalized" silica while the X indicates a lighter green silica with black dendrites. These are the source of Kansas "moss agates".
Localities that mineral collectors commonly overlook
are the Pleistocene sand and gravel deposits situated along the major river
systems in the western part of the state, especially the Republican, Arkansas,
Smoky Hill, and Saline Rivers. These streams have cut through and eroded the
Ogallala Formation and then deposited their load (as current drops in velocity)
in flood plains and channels. Today
these deposits are often well-exposed in numerous sand and gravels “pits”. If these excavations are not available,
simply walk the stream beds---See Blog Posting June 4, 2011. The "moss opal" or "moss agate" from Gove County Kansas. This slice is more of a dendritic chalcedony and is not very "opalized." Width ~4.3 cm.
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I have found a variety of minerals in the gravels
with the finest being various shades of jasper ranging from red to orange to
green to brown. Some of these jasper
specimens represent silicified chalk from the Cretaceous Smoky Hill Chalk.
These original jasper outcrops are scattered across northwestern Kansas
and seem to represent a post-depositional enrichment of the chalk, possibly
with some dissolution of the chalk, by ground water rich in silica. The
source of the silica—probably volcanic ash or bentonite (altered ash).
Petrified wood is fairly common in the sand and
gravels with the replacing material seemingly jasper rather than
chalcedony. Fossil fragments from the
Cretaceous rocks are numerous as the prismatic structure of Inoceramid shells (large
Cretaceous clams) are quite durable, and occasionally a “shark’s tooth” turns
up. Of additional interest are the
“Kansas Diamonds”, pieces of rounded crystalline, often clear, quartz. I find it interesting that most quartz
fragments are quite rounded while the jasper is very angular. Feldspar fragments are common but are much
smaller in size that the various quartz minerals.
I have seen beautiful faceted specimens of quartz
derived from “Kansas Diamonds” and combined with silver settings in quite
spectacular jewelry settings. In
addition, the jasper makes wonderful cabochons or just plain tumbled stones. Native
Americans often used the silicified chalk for projectile points and one sees
the terms Niobrarite or Smoky Hill Jasper used in the literature.
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Silicified
chalk (Smoky Hill Chalk) or jasper collected from Pleistocene gravels, Trego
County.
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And finally, the rockhound scouring
Kansas always has the opportunity to find a meteorite, or at least a
fragment. Nearly 150 meteorites are
known from Kansas (Washington University, 2011) including one located in 2005
that weighed in at 1400 pounds (part of the Breham fall). Check out the website: www.kansasmeteorites.com/.
In summary, Kansas is a state that
many non-local rockhounds overlook in their quest for interesting
specimens. However, there are numerous available
sites that provide a variety of minerals.
REFERENCES CITED
Frye, J. and A. Swineford, 1946, Silicified Rock
in the Ogallala Formation: Kansas Geological Survey Bulletin 64, pt. 2.
