Thursday, January 3, 2013

BOOK CLIFFS: BARITE

TINY, GEMMY, TERMINATED BARITE CRYSTALS PERCHED ON MASSIVE BROWN CALCITE AND PARTIAL, NERLY CLEAR CALCITE CRYSTALS.  HEIGHT OF SPECIMEN ~3 CM. 

The Book Cliffs are one of the most recognizable landforms in western Colorado and eastern Utah .  For about 200 miles this escarpment extends from where the Colorado River descends south through DeBeque to Price Canyon near Price, Utah.  The lower slope exposes marine shales of the Cretaceous Mancos Shale while interfingering sandstone beds of the upper Mancos and overlying Mount Garfield Formation (generally referred to as the Mesa Verde Group or Formation) were deposited in fluvial (stream), swamp, flood plain, and near shore marine environments.  The sandstone units capping the cliffs are fractured with vertical joints that reminded some long forgotten person of a row of books.  In the area of economic geology, the Book Cliffs contain important reserves of coal.  Positioned on top of the sandstone, but usually situated back from the edge, are various early Tertiary rock units, for example the Green River Formation and the DeBeque Formation. 

BOOK CLIFFS NEAR GRAND JUNCTION, COLORADO.
The Mancos Formation and its stratigraphic equivalent to the east known as the Pierre Shale, often contain concretions.  Many times these concretions are quite fossiliferous while others contain beautiful crystals of barite and/or calcite.  For example, concretions weathering from the Pierre near Wasta, South Dakota (east of Rapid City), yield a variety of cephalopods in addition to spectacular crystals of golden barite.  Many years ago our field trip leader took us to a Mancos locality on the east side of the San Rafael Swell south of Price, Utah, where participants collected a variety of clams and cephalopods.  Although rare, concretions in the Pierre near the Kansas-Colorado state line along the Smoky Hill River give up some nice barite and calcite crystals.  However, some of the most spectacular barite crystals are those collected from concretions in the Mancos Shale in the Book Cliffs near Grand Junction, Colorado.

BROKEN CONCRETION IN MANCOS SHOWING WEATHERING BACULITE CEPHALOPOD. 
I decided to hunt the exposures near Grand Junction during a camping trip to Colorado National Monument (one of my favorite places southwest of town).  I had been there years before hunting for fossils but this time checked with a local rock shop about prospective collecting sites.  The employee essentially directed me north from Grand Junction on gravel/dirt roads until the trails stopped and public land was available.  I then begin to hike up the slope banging on concretions as I found them.

It was not long before it became apparent that perhaps I was not the first collector to bang on the rocks—most concretions were cracked and broken!  So, I checked my water supply and headed up the slope and away from the roads, still banging on the rocks.  The first thing that I noticed was that some of these rusty colored concretions were “really large", like 6-7 feet in diameter.  The second obvious item was the large number of straight-shelled ammonites, Baculites sps. weathering out of the concretions.  I collected a few and noticed that most were steinkerns, or internal molds, and they did not exhibit remnants of the external shell.  However, some of the specimens displayed nice suture lines.

The first crystals that I found were pieces of calcite, then lots of calcite!  But, I was looking for the spectacular water-clear crystals of barite, and they soon appeared.  These specimens are beautiful, usually prismatic, nicely terminated, gemmy, and water clear; however, some crystals with a yellow tint have been reported.  The ones that I collected were small, mostly less than 3 cm., but “nice”.

GEMMY, TERMINATED, WATER CLEAR BARITE CRYSTALS; HEIGHT OF SPECIMEN ~2.2 CM.  
It is my understanding that the crystals have been collected for decades, but are still available for those collectors willing to take a little hike and bang on the rocks.  


HEIGHT OF CRYSTAL ~2.2 CM.








1 comment:

  1. Nice finds! I live 8 miles from the main digging area and I have mostly found crystals on the surface. Either left behind by previous rockhounds who did not want them or they eroded out of the concretions. It takes a lot of work to find good specimens in the concretions (Out of 4 concretions I opened, only one had some barite crystals in it!!)! You can check out my finds on my wordpress blog:
    http://rockhoundgj.wordpress.com/
    Good to see some CO Springs rockhounds enjoying our beautiful gems here! I am jealous for those who live close enough to get Pikes Peak Batholith Amazonite/Smokies. :-)
    -Ranger Derek

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