Wednesday, February 20, 2019

BRUCITE: EXPLORING TUCSONS SHOWS


The line was in place before the opening bell at Tucson's New Mineral Show.


Buyers scrambled to fill their boxes at Shannon's.
 
The next morning, Day 2, I was up bright and early and headed to the opening of Tucson’s New Mineral Show that was held at the site of a former “slaughter house.”  I was interested in getting to one of my favorite mineral dealers, Michael Shannon.  His shop happened to be in the former corral, a holding pen prior to the poor suckers heading to the hamburger house.  Unfortunately (for the mineral shows) the rain came again over night and parking was muddy and wet.  Although I arrived 20 minutes before opening, the line was stretched out into the street waiting for the bell!



One of the things that I like about Shannon Minerals is the ability to locate some very rare species.  My philosophy over the last several years has been to purchase specimens that are uncommon and priced fairly (probably cheap).  Mike has often provided these minerals. 
For the last couple of years, maybe a few more, a bright lemon-yellow botryoidal mass has graced the tables of many mineral dealers.  Prices on some of these specimens range into five figures and small time collectors like me need to hunt and hunt for more reasonably priced specimens.  There seems to be an abundance of golf ball-size specimens that sell for one hundred dollars to over one thousand dollars-prices vary. The mineral in question is brucite, a magnesium hydroxide [Mg(OH)2].  As best that I can determine, collectable brucite is not a common mineral and “natural” brucite has little commercial value except perhaps as a source of magnesium.  However, synthetic brucite is useful as a flame retardant and insulator. 


I may remember brucite from days gone past as sort of a non-descript “crud” present in some metamorphic rocks.  I fact, I thought brucite was some sort of a clay mineral, perhaps due to its common association with clay minerals like montmorillite and smectite, and some of the chlorite group minerals.  At any rate I did not pay much attention to brucite, that is until the mineral suddenly appeared on the scene selling for “big money.” 


So, what is the deal? My best answer is that a new locality in Pakistan (Killa Saifullah District, Baluchistan) showed up producing some brightly colored “lumps” of a “pretty” mineral, bright lemon yellow to pastel yellow—and the rest was history.  Brucite became collectable and the larger the specimen the better.  Yellow was in!

In parts of the world where geological work my be completed without risking one’s life, geologists know that brucite may form when dunite (olivine-rich rocks derived from the Earth’s mantle) is subjected to serpentinization (hydration and metamorphism common at plate boundaries), when periclase (magnesium oxide, MgO) in marble hydrates, and when certain limestones undergo low temperature alteration.  My only clue to the Pakistani brucite is that some photos in MinDat show a serpentine matrix so I would assume the brucite is associated with metamorphism. 

Some brucite is an attractive display mineral, no doubt about it. I tried location information about the yellow color; however, I found mostly speculation rather than facts,  I suppose the answer is out there but locating such is above my pay grade.
Botryoidal mass of brucite with pronounced pearly luster.  Width of specimen ~1.2 cmPurchased at Shaannon's.


Besides the yellow color of collectable brucite the mineral is found shades of drab grays or blue-grays, green, and white to clear although manganese, zinc and iron impurities may offer other colors.  It is quite soft ~2.5+ (Mohs), translucent to transparent, vitreous to pearly luster, and a white streak.  Some specimens show fibrous crystals or tabular pseudohexagonal crystals.  Brucite can be massive, botryoidal with crystals that are indistinguishable, bladed, grainy, or other habits. 

Multicolored specimen of brucite purchased at Shannon's. Note the crude rosette of fibers.  Width of specimen ~1.5 cm.

I stayed away from this vendor!


I wanted, but could not afford, these variscite phosphate nodules from the Little Green Monster Mine in Utah.

Friday, February 15, 2019

BIG FOSSILS: EXPLORING TUCSON SHOWS


The Mineral and Fossil Marketplace, with minerals featured in the last article, also has vendors with a nice displays of fossils.  Imagine my surprise when I walked into Sahara Overland, expecting lots of fossils from Africa, and was greeted by a nice mosasaur collected from the Smoky Hill Chalk in western Kansas!  Platycarpus, a large swimming marine lizard,    is limited to rocks of the Late Cretaceous and lived ~ 84-81 Ma. and its fossils are extremely abundant (for large vertebrates) in western Kansas.  There is much information about mosasaurs and other Cretaceous fossils on the web site www.oceansofKansas.com, plus the second edition (2017) of a book by the same name.






Upon entering another large room, I was able to observe additional fossils that I wanted to take home; however, my office certainly could not accommodate such large specimens!


Dunkleosteus was a large swimming animal (commonly called fish in a generic term) termed a placoderm (plate + skin = armored) that certainly was the top predator in Late Devonian marine waters.  They were up to 20 feet in length and had bony chomping jaws (termed a tooth plate) rather than teeth (like most modern “fish”) and two bony “fangs” protruding from the top of the upper jaw.  Their head was covered by bony plates that articulated with plates covering the remainder of the body. They did not have a bony internal skeleton.  They were true superpredators living around the time period of 358-382 Ma but did not survive extinctions at the end of the Devonian.


Basilosaurus was a toothed whale that lived in the later part of the Eocene Epoch ~40-35 Ma.  Specimens recovered indicate some of these animals reached 60 feet in length.  That is one big predator.  When first described by paleontologists Basilosaurus was thought to be a large reptile and acquired a moniker meaning King Lizard.  Later paleontologists noted mammalian traits of the beast such as two-rooted molars.  Basilosaurus may have a lineage showing descent from land mammals since a rudimentary set of hind limbs are present.  Both Mississippi and Alabama have deemed Basilosaurus as a notable animal and named them as their State Fossils.
 

Cervalces was is a type of extinct deer commonly known stag-moose or elk-moose.  Arriving from Eurasia they inhabited North America during the later Pleistocene Epoch (the Ice Age, last couple of million years) and probably lived in wetlands south of receding glaciers. Most fossil bones are found in the Midwest part of the U.S.  They did not survive the late Pleistocene extinction and seemed to be ecologically replaced by our modern moose (Alces alces).


A large cat known as the saber-toothed tiger is one of the most famous “prehistoric animals” (ranking up there with T. rex) and every child’s idea of the villain animal chasing down baby mammoths and frightening small cats and dogs as it gobbles down its prey. It (Smilodon sp.) is not a true cat (as is a modern lion) nor related to tigers nor was the first “saber-tooth cat.”  However, it does belong to the cat family, the Felidae, lived in the Pleistocene, and became extinct at the end of that Epoch. Smilodon is the State Fossil of California due to the many specimens found at the Rancho La Brea tar pits in Los Angeles.

 

Crinoids are members of the Phylum Echinodermata (spiny skin), related to animals like starfish, and are rather uncommon in modern oceans.  However, in shallow waters of the Paleozoic Era crinoids were one of the most common animals.  Early paleontologists thought they were plants that grew attached to the sea floor by a stem.  In reality, they filter out microorganisms and are animals. Only a few groups survived the great End of Paleozoic extinction event.

So, that was my foray into paleontology that finished my first day exploring Tucson.  Lots more to see.

Tuesday, February 12, 2019

UTAH WULFENITE: EXPLORING TUCSON SHOWS




February has rolled around again, and the month is special for Groundhog Day, Valentine’s Day, A. Lincoln’s and G. Washington’s birthdays rolled into President’s Day, Chinese New Year (2020 is the Year of the Pig), and the Tucson Rock and Gem Shows.  Of course, the latter is my favorite although I certainly respect the birthdays of our most famous presidents.
The Tucson shows occupy the first two weeks of February and culminate in the official Tucson Gem and Mineral Show (known as the main show) that is held in the downtown Convention Center on February 14-17.  Scattered around town are nearly 50 other “official” shows and venues.  Some of the ancillary venues are quite large with hundreds of dealers selling their minerals, rocks, fossils, coon tail hats, lotions better than Botox, and a wide variety of “you name it.”  However, most of the venues are related to geology, except perhaps the African Village. 

In addition to the large venues there are many smaller shows with perhaps a dozen or so dealers.  However, small does not always relate to less expensive minerals and rocks---some are very high end such as the Westward Look Mineral Show.

My first day at the "Show" (refers to any of the venues) was on Monday the 4th since I arrived in town somewhat “late.”  On that particular day I had planned to hit a couple of outdoor shows where sellers are dealing out of small popup tents, or small RVs, or whatever but the tables are exposed to the elements ( I refer to them as mom & pop shows).  From what I understand this is how the smaller ancillary shows started out decades ago, before the advent of tents as large as a football field. Monday was also the day it decided to intermittently rain and I was soaked more than once.  I felt rather sorry for the dealers, but most come back year after year and just take the weather as it comes.



·       When I first attend the Tucson shows there were many of the ancillary venues that looked like this---put out the tables, maybe a popup cover and have your camper parked behind the goodies.  Unfortunately, most of the mom and pop shows have disappeared from the scene.
This was a fantastic specimen as it is a polished slab of a phosphate nodule collected from near Lucin in northwestern Utah.  The green is variscite, while the gray is is probably wardite, and others are too small to identify.  It resembles those nodules from the Little Green Monster Mine once operated by Ed Over and Art Montgomery.

When the rains come, cover the mineral specimens and let the honker rocks get wet.  Maybe they are yard rocks anyway.
 
Can’t get away for lunch?  Fire up the propane cooker.
Want to guard you wares at night? Don't want to spend your small profits? Pitch the tent with a rain guard. 
 The Miner’s Coop is one of the first shows that visitors might see coming in from the north on I-10; however, it is one of the most difficult to reach as the two major exits have been closed for at least 2-3 years due to construction.  On my visit the crowd was sparse as the rain and mud put a damper on the selling and dealers were playing a cat and mouse game of pulling off tarps to expose their goodies and then covering the tables to try and keep them somewhat dry.  I did talk to Kim and Bodie (with their amazonite and quartz) from the Lake George region, a seller from Fountain and one from Pagosa Springs.  I really did not see all of the specimens available, due to covered tables, and so moved on without a purchase.
Blue crystals of rare boleite, a complex, hydrated lead-silver-copper oxychloride offered by Jack Crawford.
 My second stop, Mineral and Fossil Marketplace, is also a favorite of mine mainly due to the presence of a dealer by the name of Jack Crawford.  Now Jack does not know me from the man in the moon but does recognize me from past years and if questioned, regales me with stories from his many years of collecting in Mexico.  He is a great person to visit with and someone with a terrific knowledge of geology, especially mining and minerals. He also has some of the finest crystals of boleite (hydrated lead-silver-copper oxychloride).  I have purchased some smaller crystals in past years as they are rather rare; however, this year he had much larger crystals and therefore out of my price range (see Posting June 22, 2016).

The second reason for a stop was to admire the wares sold at Australian Outback.  Now, I am not a collector of “slabs” or lapidary rough but do like to ogle the nifty displays from Australia.  
I always enjoy Australian Outback’s display of  siliceous mookaite.  The rock is collected from the Windalia Formation (Cretaceous) in western Australia and is actually a radiolarite (according to MinDat) where the silica originated from ginormous numbers of single celled organisms called radiolarians.  These little creatures have a “skeleton” of opal (form of silica).  However, Australian Outback believes that water percolated through a radiolarite and deposited silica, often in the form of chalcedony rather than opal, in overlying layers and during the way picked up iron oxides for color.


Tent at Australian Outback keeping rain off the valuables at Mineral and Fossil Marketplace.

These nicely polished, shiny slabs are marketed as Black Jade.  They are an amphibole and a form of the mineral actinolite, a calcium-magnesium-iron silicate. Nephrite is also an amphibole and is one of the two minerals commonly called green jade.  So, is this jade?  Don’t know as it could be nephrite included by black minerals.  I assume Black Jade is a trade name.
I had always seen kunzite, a pink spodumene or lithium aluminum silicate, as nice gemmy pink crystals used as faceted gemstones.  These slabs are marketed as such and are also sold as polished cabs.  I could not locate other information.

This petrified wood is marketed as peanut wood. The wood has a dark color with numerous infilled white borings due to a marine boring clam called Toredo.
A geode with inner celestine crystals offered by a Madagascar dealer.
I also was able to nab a specimen of wulfenite collected from Utah and was interested in the specimen for a couple of reasons.  First of all, wulfenite is the theme of the Tucson main show this year (Wulfenite is Loved) and second, I have an interest in minerals from Utah.  In addition, both Rock and Gem and Rock and Minerals devoted their recent journal editions to the mineral and forgot to mention collecting from Utah! 
Wulfenite is probably one of the most easily recognized mineral among any amateur rock hound and one of the most collectable by hobbyists from all ranks, newbie to professional (7206 photos on MinDat). It is a beautiful mineral and easily adorns specimen shelves across the collecting community.
A lead molybdate [Pb(MoO4)], wulfenite is famous for its common habit of forming thin tabular crystals, often transparent (but ranging to opaque), that occur in various shades of orange to red to yellow (uncommon as green or brown or blueish or black (see Posting April 20, 2017) and “butterscotch” is a common color descriptor.  There is some disagreement about the color changes although minor chromium probably acts as a red or yellow chromophore.  Crystals often have a vitreous luster and will easily reflect light as a mirror.  Others are much “duller” and have a resinous luster; some are covered by various druzes.  The streak is a nondescript white. Wulfenite is quite soft at ~3.0 (Mohs) and the crystals brittle.  Besides the thin tabs, pyramidal (and bipyramids) and stubby crystals are common and often confuse new collectors who are used to orange or yellow tabs. 
Wulfenite is a secondary mineral deposited in the oxidized zone of lead ores; it seems particularly common in the state of Arizona and Bladh (2019) noted at least 275 collecting localities.  Although collectors love isolated and single crystals the vast majority of  wulfenite probably occurs as granular or intermixed masses. 

Wulfenite is much less common in Utah, than Arizona, and therefore “finds” at shops or mineral shows are exciting.  My particular specimen (shown above with crystalline calcite, width ~4.0 cm) picked up from this show was collected at the Tecoma Hill locality in Box Elder County, an area in the extreme northwest region of the State and former sites of lead-zinc-molybdenum exploration.  Most of the ore seems associated with Tertiary igneous rocks intruding Paleozoic limestone.

REFERENCES CITED

Bladh, K., 2019, Arizona Wulfenite: Rocks and Minerals, v. 94, no. 1





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