CRANDALLITE: TUCSON GEM SHOW REPORTS & PALEO

Tuesday in Tucson was a paleontological day—more of a viewing day.  I collected thousands of vertebrate fossils over my career in academe and all were added to museum collections as most were taken from federal lands with permits.  Almost all were very small mammals or reptiles that could fit in small vials and your front shirt pocket—I was not a collector of dinosaurs or large marine reptiles.  At one time I collected some large musk oxen and a few other things; however, that seemed like a heavy lifting task, especially when digging and plastering were involved.  But today, I still enjoy looking at some of these fantastic specimens.

 

Dunkleosteus shull.

There are tens of thousands of Moroccan invertebrate fossils on the Tucson marketplace including trilobites and cephalopods by the truck load.  However, I often am quite confused about the authenticity of many of these specimens!  Many seem “to good to be true,” for example when starfish are plopped in the middle of a slab of trilobites, or when every appendage detail is visible on a trilobite.  Perhaps all is well and I am a pessimist.  However, I would certainly not pay some rather high prices without a detailed examination under magnification.

 

Trilobite: $500.

Nice brittle stars!

Nice crinoid slab.

Trilobites and brittle stars.  What are the chances?

Wow.  Big teeth.

Crocodilian object d’art.

Very interesting.

Spheres anyone?

The palm frond fell in with the fish.

Ammonite object d’art with added copper.

I noticed that many of the large vertebrate fossils contained an appreciable amount of “plaster” (or some more advanced filler).  That fact is not readily disclosed by many sellers.  I would liken these products to some of the gem sales---respectable dealers will disclose if a particular gem is synthetic, oiled, filled with glass paste, or a variety of other sorts of things.  Or, is it “buyers beware?”  There is nothing wrong with plaster/filler if such details are disclosed.

What about my $5 or less mineral of the day?  I am fascinated by the arsenates, phosphates and vanadates and especially those collected from some of my favorite states—like Utah.  So, I was quite pleased to pick up a partial nodule of crandallite. 

Nodule of yellow crandallite with a few “white” eyes of wardite.  Width ~ 6.5 cm.

Crandallite is a rather uncommon hydrated calcium aluminum phosphate [CaAl₃(PO₄)₂(OH)₅-2H₂O] that often is associated with the phosphates variscite and wardite.  I suppose that when most rockhounds think about collectable and colorful crandallite and variscite, the Little Green Monster Mine in Utah County, Utah, pops up, along with the names Ed Over and Art Montgomery.  Over was a mineral collector from Colorado Springs and teamed with college professor (Lafayette College) and mineral dealer Art Montgomery.  Together in a few short years the dynamic duo brought to market and museums pounds/tons of spectacular mineral specimens including topaz from Pikes Peak, red wulfenite from the Red Cloud Mine in Arizona, various minerals from the high altitude Mt. Antero, Colorado, green epidote from Prince of Wales Island in Alaska, and the variscite from Fairfield, Utah (near the south end of the Oquirrh Mountains).  They worked the Little Green Monster Mine for a few short years in the late 1930s and brought out the colorful phosphate nodules by wheelbarrows.  Today the mine is closed and all Little Green Monster Mine specimens are decades old and many are really quite expensive (four to five figures).  My specimen seemed like a real bargain!

Variscite [AlPO₄-2H₂O] is the original phosphate and forms in dense microcrystalline nodules with trace amounts of chromium and phosphorous imparting the green color.  Crandallite seems the first alteration mineral to form as variscite picks up and adds calcium from solution.  Normally colorless, trace iron gives the Utah crandallite a yellow color.  Numerous other exotic phosphates such as wardite, englishite, gordonite, millisite, montgomeryite and overite are also present at the Little Green Monster.