TUCSON 24: MONTGOMERYITE (BLACK HILLS SD) FROM AN OLD TIMEY SHOW

 

55 or so dealers spread out at the Miners Coop Show

One of the many Tucson shows that I make time to attend is the Miners Coop Rock Show. This venue seems to be the most western and most northern show situated at Mike Jacobs Sports Park at the corner of Ina Road and I-10. The location is away from the hustle and bustle of the major venues in and near the city center, southeast near the Kino and Holiday Inn Shows, along the Oracle road and I-10 motel strips and the 22^nd street monster. The Coop show is a mom & pop, old timey show where vendors are outside or small open tents displaying thjeir wares.  Don’t worry about a rainstorm, of which are numerous, just throw a tarp over the specimen tables and retreat to their small RVs parked behind the tables. The show is described as the people who dig and mine and the home of the diggers and do-ers. 

 

All sorts of rocks, minerals, and fossils for sale.

Not all minerals are what they appear to be! m This is a sack of nice fresh oak acorns.

The vendors are likely to be perched on a lawn chair and snoozing in the sun but are more than willing to engage in a lively conversation. These are the vendors who may have come from a month in Quartzite and may be heading to February/March New Mexico shows in Los Cruces, then Deming,  Albuquerque, Santa Fe, and Truth or Consequences—any place to avoid snow shoveling back at their home base. 

Kim and Bodie from Runnin Boar Minerals sell a variety minerals including amazonite from their quarry.

 
Generally speaking the vendors are about the same each year and I enjoy talking to a parrot from Arkansas, the azurite blueberry dealer from Moab, and Kim and Bodie from Divide, Colorado, just up the road from my home base in Colorado Springs. No expensive motel rooms or giant tents or the convention center –just a bunch of friendly diggers and do-ers! 

What I found at the show was small box, still partially damp from a rain, that had been tossed in a flat of minerals with other specimens. Always curious, I pulled out my loupe to take a peak at the specimen labeled “ montgomeryite, Tip Top Mine, Black Hills”.  Wow. I zealously guarded the box and continued to peak at others but none piqued my interest. “How much do you want for this mineral? How about three bucks.” I hesitated but pulled out the money and was happily on my way. I had previously blogged about the mineral a couple of times. However, montgomeryite is a pretty rare secondary phosphate named for Arthur Montgomery and is associated with Colorado Springs, the Black Hills, and Utah—three of my favorite places.

In 1940 E.S. Larsen of Harvard University described two new minerals collected from phosphate nodules near Fairfield, Utah.  Larsen had been working and describing minerals from this area for at least a decade and finally “got around” to formally naming the hydrated calcium magnesium aluminum phosphates: overite [CaMgAl(PO₄)₂(OH)-4H₂O], named for Edwin Over of Colorado Springs, and montgomeryite [Ca₄MgAl₄(PO₄)₆(OH)₄-12H₂O] for Arthur Montgomery of New York City.

Over and Montgomery had spent part of the years 1936-1940 prospecting and mining phosphate nodules from Clay Canyon near Fairfield in the Oquirrh Mountains southwest of Salt Lake City. They were mainly after variscite, a beautiful green, hydrated aluminum phosphate [AlPO₄-H₂O] that was sliced for mineral collectors and cabbed for jewelry. However, these nodules also contained a plethora of micro minerals that were of great interest to collectors. Today the Fairfield site is closed and remediated or perhaps open to the claim owner every few years?

Today, the best-known montgomeryite crystals are found from a few mines in the Black Hills of South Dakota, especially the Tip Top Mine near Custer, formally a lithium mine in pegmatites associated with the Precambrian Harney Peak Granite.  Here montgomeryite generally occurs as small lath-like crystals that are flattened, striated, elongated and capped by a pyramid.   Crystals are translucent, have a vitreous luster, and a hardness of ~4.0 (Mohs).  At the type locality at the Little Green Monster Mine in Utah the crystals are generally colorless to pale green and occur in nodules that are of sedimentary origin.  At the Tip Top Mine the lath-like crystals are colorless to some sort of a red to orange to salmon to pale yellow color and are associated with several other secondary phosphate minerals and primary phosphates like triphylite as well as and the pegmatitic microcline feldspar.

Montgomery laths on a microcline matrix. Black mineral is some sort of a phosphate perhaps rockbridgeite and/or triphylite. Width FOV ~ 7 mm.

I felt fortunate to locate the specimen, especially with the low price, and will continue to seek other Tip Top and Fairfield specimens such as the millisite found at 22^nd Street show described in the February 6 post.