BLUE CHALCEDONY: TUCSON 2016

My second day of the Tucson journey was spent at the Moroccan Dealers Village on North Oracle Street.  It was a short visit day due to an important event at the State Park campground---a day know affectionately to all RV campers as “dump day!”  In my situation, this event requires moving and securing all items in the RV, closing up the slide rooms, hooking up the unit, and then slowing proceeding to the campground “dump station.”  Grab your gloves, hook up the drain hoses, back away from the “little hole to the campground's main sewer” and pull the drain plugs on the RV---and hope there is no splashing, or in the worst case scenario I have observed, having the drain hoses come loose from the RV.  Dump day is the equalizing activity for all RV campers---big ones, middle ones and small ones, hundreds of thousands of dollars to a few hundred dollars---they all need the black tanks emptied at some point!

 

The tents at the Moroccan Dealers’ Village covered nearly two lengths of city blocks.

I like to refer to these pieces of sculpted quartz as Washington Monuments.  Perhaps they are ordinary obelisks, or mystic towers.  Perhaps they are just pieces of carved quartz for designer coffee table.  Whatever, there were numerous specimens of all sizes scattered throughout the Shows.

A nice slab of Paleozoic crinoids but with much reconstruction.

Fossils are always a mainstay at Moroccan dealers.  These coiled cephalopods are saucer-size and relatively cheap.

Talk about reconstruction, not only are many of these cephalopods carved and built, they are “glued” onto the matrix.  Built for designer homes of non-rockhounds.

How many shark’s teeth does it take to fill a large flat?  I don’t have the slightest idea!

Most specimens for sale from the Moroccan dealers were either: 1) very large slabs of fossils such as the crinoids and cephalopods shown above; or 2) flats of smaller fossils (see shark teeth).  Several U.S. shop dealers were visiting the Moroccans and negotiating for large purchases; $100 bills were certainly changing hands.  I hunted through the boxes but found little of interest.  So, across the street I went---back to my Day 1 haunts (see previous posting) where I hunted through the boxes and located blue chalcedony.

 

Blue vein chalcedony from the White River Group, South Dakota.  Width of vein ~2.3 cm.

So, why would I want to buy three pieces ($2 for all three) of blue cryptocrystalline quartz?  The answer is simple, but maybe hard to explain!  I have written several postings about collecting rocks and minerals in western South Dakota, the scene of my field work for the graduate masters degree.  Today most of these degrees in science are MS Degrees (Masters of Science); however, mine was actually an AM Degree (Masters of Arts).  I don’t have the slightest idea the reason behind this little quirk.

At any rate, I wandered over countless acres of rocks described as either the Brule Formation or the Chadron Formation and collectively known then as the White River Group.  If readers have ever visited Badlands National Park, they have seen the units with an amazing fossil biota.  In addition, some of the rocks are crisscrossed by sedimentary dikes--most are clastic dikes composed of sandstone while others are dikes of blue to lavender chalcedony.  I remember picking up numerous specimens during my field work but over the years tumbled and/or gave away these beautiful pieces of chalcedony.  The blue chalcedony is easy to recognize and I have been rummaging around for cheap specimens for several years.  And, here they were in a labeled broken old specimen box and mine for the taking (actually purchasing).  Ah, my mind immediately returned to the summer of 1966 and I could hear “The Troggs” belting out the Number 1 hit of July---Wild Thing.  All adults of a certain generation know the lyrics by heart---you know: Wild thing you make my heart sing, you make everything groovy, wild thing. Come on, sing along with me!

The chalcedony veins, along with the sedimentary clastic dikes, occur at several different horizons within the Eocene-Oligocene White River Group and probably formed by a secondary processes termed diagenesis. Gries (1996) believed the chalcedony veins formed from secondary silica gel inserted into shrinkage cracks forming in the clay-rich sedimentary beds.  It appears that Native Americans utilized the chalcedony and I have recognized the mineral in projectile points.

Chalcedony is not really a separate mineral but is a variety of cryptocrystalline silica containing microscopic or submicroscopic fibers of a mixture of quartz (Trigonal Crystal System) and another silica mineral called moganite (Monoclinic Mineral System).  Over periods of time the unstable moganite converts to quartz.  I am uncertain about the age of the oldest mogenite---another one of life's persistent questions! 

Chalcedony, that seeming common “mineral” found in all sorts of sedimentary rocks in both primary and secondary environments, and sometimes in igneous and metamorphic rocks, is actually quite complex.  For an in-depth discussion, including length-slow vs. length-fast chalcedony, see the quartz page at:  www.quartzpage.de/chalcedony.html.

For an ole rockhound like me chalcedony is fairly easy to recognize due to its waxy luster becoming vitreous when polished, hardness (~6.5-7.0 Mohs), conchoidal fracture, its habits of forming mammillary masses, vein fillings (as in the Badlands) stalagmitic masses, “blobs” in geodes, or just weathered out pebbles and cobbles of waxy looking quartz.  Chalcedony is translucent and never quite transparent or opaque.  Sometimes the “mineral” is the cementing agent in sandstone or the permineralization/replacement agent in fossilized (petrified) wood.

   

As for the blue color, The Quartz Page notes “The blue tones…found in pure chalcedony are caused by Rayleigh scattering [too lengthy and difficult to explain here.  If interested I would suggest further research and reading] of light on tiny particles, the mechanism that is also mostly responsible for the blue color of the sky.”

One other thing—chalcedony, as well as agate and other varieties of microcrystalline quartz, are porous and easily dyed.  Know your dealers, ask questions, and if it looks too colorful to be real, then it probably is a "fake"!