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"!

BLUE QUARTZ: TUCSON 2016

I have taken off from Blog Postings the last month or so to get ready for the BIG event.  The days finally arrived: the opening of the annual Tucson Gem, Mineral and Fossil Shows (TGMFS).  Something like 48 different venues are scattered around town with some running for a couple of days (Gem and Jam Fest) but most operate for a couple of weeks ending the 14^th of February.  Some shows may only have 5-6 vendors; most are larger with  the “really big ones” producing vendors in the “several hundred” category.  A few venues are wholesale only but most are free and open to the public.  Some shows I visited are the “mom and pop” variety (my favorites) run out of sunshades or even open air while others are housed in gigantic permanent “tents” with concrete floors where showcases are common.  Prices range from less than $1 to hundreds of thousands.  In the 22^nd Street Show I saw quartz cabs selling for a couple of bucks while in the next door booth an opal (larger than a nickel but smaller than a quarter) was priced at $185,000.  I poked and sorted and blew dust off boxes looking for elusive mineral specimens priced at $10, or preferably below!  I also was hot on collecting “cheap” (no better word for being frugal): 1) blue minerals, the theme of the main show; and 2) minerals with names I did not recognize—not too hard for an old paleo person!

Part of the large conglomeration of the TGMFS is The 62^nd Annual Tucson Gem and Mineral Show (TGMS) commonly known as the main show ($13 admission fee; parking competitive---ride the shuttle)).  This four-day event was held at the Tucson Convention Center (February 11-14) with the 2016 theme Shades of Blue, Minerals of the World.  More on this later.

This posting, along with several following, will be my attempt at describing some of the venues along with my chase for the elusive cheap minerals.  Even with the many days spent in Tucson, it was impossible, at least for me, to hit all of the 40+ shows.

My first day in Tucson is usually spent checking out the Arizona Mineral and Fossil Show on north Oracle Street (one of the major N-S streets in Tucson leading downtown from the north).  Two of my favorite “mom and pop” dealers are there every year: Rock Deco and JaM’s Rocks.  In addition, there are a number of other dealers present who display some really large specimens---much too large for my collection but enjoyable to browse. 

Jim, the proprietor of JaM's Rocks, is a really great conversationalist and is willing to share information of his yearly trips to Baja California where he collects, and also purchases specimens from local miners.  I was salivating over some of his specimens of boleite; however, they were out of my price range.  

Rock Deco next door is a great place since hunting through the boxes always turns up surprises.  This year I purchased my first specimen of a blue mineral---blue quartz described below-- for the sum of $3.

Madagascar Treasures offers a wide variety of large specimens including the ubiquitous amethyst cathedrals (shown below) from Brazil.

These slabs of petrified wood are amazing--large and heavy.  The best that I could ascertain about their provenance is somewhere in Indonesia. 

Tiger Eye is a semi precious gem that is often used in less expensive rings and pendants.  However, these large thick slabs, collected in western Australia, seem relatively uncommon.  The dinner plate size slabs were priced at ~$17, a good price. 

This is an interesting specimen of a radiolarite, a siliceous chert-like rock with the silica coming from the tests (shells) of microscopic single-celled organisms called radiolarians.  In addition this unit, collected from the Cretaceous rocks of Australia, has been broken and re-cemented--a brecciated radiolarite. 

A specimen of Australian Mookaite quarried (Mooka Creek) from near the radiolarite location in western Australia.  According to the miners this "chalcedonic variety" (as opposed to opalite and chert varieties) is the best for cutting and polishing.  They also believe the chalcedony is secondary silica absorbed into a radiolarite.  The colors are spectacular.

So my find for the day was a specimen of blue quartz collected from the Keystone Traprock Quarry in Cornog, Chester Co., Pennsylvania.  I was uncertain about the blue chromophores coloring the quartz since I remember from my eons-ago mineralogy course that blue was not a natural color found in quartz!  So now what?  Well, just in time for the Show was the publication of Rocks  and Minerals dedicated to “Shades of Blue.”  Skalwold and Bassett (2016), in a fascinating but complex article, noted that “blue quartz has not been found in nature so far, though some types of amethyst can be treated to turn blue…Natural quartz may appear blue due to inclusions of blue minerals”…Blue quartz from Minas Gerais, Brazil, is “colored by inclusions of elbaite, variety indicolite.”

MinDat.org noted that blue quartz "owes its colour to inclusions, commonly of fibrous magnesioriebeckite or crocidolite.  The color may be caused by the color of the included minerals or by Rayleigh scattering of light at microscopic inclusions." 

According to MinDat the Keystone Traprock Quarry is "a crushed stone quarry in Precambrian (Grenville) amphibolite gneiss [a metamorphic rock found at convergent plate boundaries where regional metamorphism created great heat and pressure] within the Honeybrook uplift. The mineral assemblages for which this locality is well known, are the product of alpine cleft type hydrothermal recrystallization ['Alpine-type fissures are cavities that have opened during tectonically caused stretching and bending of the rock. The cavities are entirely enclosed by the surrounding host rock...Alpine-type fissures can only form under special conditions that are not easily met. They form when rocks get folded or sheared at great depths and at relatively high temperatures, between 200° and 600°C. Under these conditions the rocks are still solid, but malleable, so they do not shatter when they get deformed slowly' www.Quartzpage.de]. Operations [at Keystone] started in 1907, but the quarry is now (2014) water filled."

 

Blue Quartz, along with patches of milky quartz and a faint gray smoky quartz, collected from the Keystone Traprock Quarry.  Width ~4.2 cm.

The specimens, like mine, seemed to have been collected in the 1970s or maybe the 1980s.  Most "modern" specimens have come from adjacent drainages and are abraded.  The problem is I cannot definitively identify the source of the blue coloring--what are the inclusions?  However, my best guess comes from information provided by Mark Jacobson (2016) who noted that Star Blue Quartz is the state gemstone of Alabama and comes from metamorphic rocks of the Inner Piedmont and Blue Ridge Provinces of the Appalachian Mountains.  These Provinces extend into Virginia where the blue color of the quartz is thought (Wise, 1981) related to Rayleigh wave scattering by abundant submicrometer-sized rutile or ilmenite inclusions. Evidently the blue quartz known as Llanite from Texas is also associated with ilmenite and/or rutile (Zolensky and others, 1988). My specimen is a nifty blue specimen and started off my hunt with a "bang"! 

REFERENCES CITED

Jacobson, M.I., 2016, U.S. state gemstones that are blue: Rocks and Minerals, v. 91, no.1. 

   

Skalwold, E.A. and W.A. Bassett, 2016, Blue minerals: exploring cause and effect: Rocks and Minerals, v. 91, no.1. 

Wise, M.A., 1981, Blue quartz in Virginia:  Virginia Minerals, v. 27, no. 2.

Zolensky, M.E., P.J. Sylvester, and J.B. Paces, 1988, Origin and significance of blue coloration in quartz from Llano Rhyolite (Llanite), north-central Llano County, Texas: American Mineralogist, v. 73.