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 cm.  Purchased 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.

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.