COLLECTING AT THE GATOROSA

SMOKY HILL JASPER

Rockhounds seeking interesting minerals for their cabinets, or looking for specimens to cut and polish, often blaze across Kansas to better “picking grounds”.  However, they may be overlooking numerous collecting possibilities.

In western Kansas the Miocene Ogallala Formation crops out at many localities.   This unit, consisting of stream gravels, along with a few volcanic ash beds and lake deposits, represents debris shed off the rising and eroding Rocky Mountains to the west, as well as fragments of local Cretaceous rocks.  As such, these outcrops contain a wide variety of minerals that originally formed in igneous rocks of the mountains.  The problem in collecting such minerals is that the Ogallala outcrops are commonly consolidated and tightly cemented and many times are covered by younger wind-blown sediments.

The answer to locating interesting minerals, and one that collectors commonly overlook, is to examine sand and gravel deposits situated along the major river systems, especially the Republican, Arkansas, Smoky Hill, and Saline, in the western part of the state.  These rivers have cut through and eroded the Ogallala and underlying Niobrara formations and then deposited their load (as current drops in velocity) in flood plains and channels.  Today these Pleistocene sediments are often well-exposed in numerous sand and gravels “pits” found on the older terraces.   If these excavations are not available for searching, simply walk the stream beds.

I have found a variety of minerals in the gravels with the finest specimens being various shades of jasper ranging from red to orange to green to brown.  Some of these jasper specimens from along the Republican, Smoky Hill, and Saline rivers in northern Kansas represent silicified chalk from the Cretaceous Smoky Hill Chalk Member of the Niobrara Formation.  These 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 and chalcedony occurs in a variety of colors.  Of additional interest are the “Kansas Diamonds”, pieces of rounded and egg-shaped crystalline quartz.  Feldspar fragments are numerous but seem much smaller in size that the various quartz minerals (~1 cm or less) and are generally angular (broken along cleavage planes).  In addition, sort of nondescript dark colored rocks with an obvious igneous source are locally abundant.

The quartz minerals derived from the Rocky Mountains are generally less than 5-6 cm and highly rounded as the transport distance is great.  The locally derived jasper may be large (up to 13 cm in my collections) and specimens are angular.

I have seen beautiful faceted specimens of quartz derived from “Kansas Diamonds” and when combined with silver settings are quite spectacular.  In addition, the jasper makes wonderful cabochons or just plain tumbled stones.  Native Americans often used the silicified chalk for projectile points and one see the terms Niobrarite or Smoky Hill Jasper used in the literature.

So, although gemstones and semi-precious gemstones are essentially non-existent in Kansas, the jasper, chalcedony, quartz  and petrified wood offer some nice specimens for the lapidariest or flintnapper. 

BTW, the Gatorosa is my brother's ranch along the Smoky Hill River in Trego, County!

mike 

LOCALLY DERIVED SMOKY HILL JASPER.  MANY SPECIMENS SHOW STRONG BANDING.

NON-LOCAL CHALCEDONY.

NON-LOCAL? CHALCEDONY.

SAND AND GRAVEL DEPOSIT ON THE "HIGH TERRACE" AT THE GATOROSA.  YUCCA PLANTS FOR SCALE.

ARTIFACTS CONSTRUCTED FROM SMOKY HILL JASPER.  PHOTO COURTESY OF DON BLAKESLEE AND KANSAS STATE HISTORICAL SOCIETY.