BLACK HILLS PHOSPHATE: MONTGOMERYITE; A CONNECTION TO CSMS

The Colorado Springs Mineralogical Society recently celebrated its 82^nd birthday as the group may be traced to November 24^th, 1936.  A Charter Member of the organization was a young mineral collector by the name of Edwin Over.  Mr. Over had recently met a young (b. 2009) and more affluent collector by the name of Arthur Montgomery (from New York) and in 1934 they became business partners and started collecting and selling minerals. Wilson (2018) noted that at times they worked together collecting in the field but often Over worked alone and sent specimens back to New York where Montgomery would market them. 

They seemed to have remained partners until the early 1940s when Montgomery sold his share of the partnership   and retired from the mineral market business. However, during that 7 year period the two collectors brought to surface an amazing number of world-class specimens including red wulfenite from the Red Cloud Mine in Arizona, epidote from Prince of Wales Island in Alaska, variscite and other phosphates from Fairfield, Utah, and beryl (aquamarine), phenakite, albite, bertrandite and fluorite from the lithium-rich pegmatites on Mt. Antero located southwest of Buena Vista, Colorado. The latter specimens were collected during a six-week period in summer 1938 (Wilson, 2018).

During World War II Montgomery leased/purchased the Harding Mine in New Mexico and brought to surface tantalum, beryllium and lithium that he sold to the U.S. government. Sometime after the War Montgomery donated the mine to the University of New Mexico for use as a teaching experience and mineral collecting area.  During Montgomery’s time at the Harding all profits went to support various activities in the nearby small town of Dixon.

After the War Montgomery started a Ph.D. program at Harvard and graduated in 1951.  He then joined the faculty at Lafayette College in Pennsylvania where he spent his academic career, retiring in 1976.  But Art was nor finished with living a productive life and for a five-year period he volunteered at the Trinidad State Nursing Home before moving to Albuquerque, New Mexico, where he spent the remainder of his life (d. 1999) working/volunteering at a Christian organization helping others. 

Montgomery had a large and fabulous mineral collection that he gave to individuals and institutions including the Smithsonian Institution, Harvard University, Princeton University, the Royal Ontario Museum, and Acadia University. In the early 1970s Montgomery provided financial resources to start the journal The Mineralogical Record, and the organization Friends of Mineralogy. It also seems that Montgomery was quite interested in botany and was one of the five founders (in 1959) of the Montgomery Botanical Center in Florida and served them until his death.

If interested in additional information about Montgomery’s life see Volume 8, Number 2 (2000) edition of The Matrix, a Journal of the History of Minerals.

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. In fact, in 1930 Larsen had described what later became overite as “Mineral Number 8.”  

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. Previously the two collectors had been in Alaska gathering epidote crystals from Green Monster Mountain.  Upon arriving in Clay Canyon, they dubbed their mine the Little Green Monster.  Evidently Montgomery did most of the selling in New York City but also gifted several of the nodules to the Smithsonian Institution where they are preserved and displayed.  Today museums and collectors often pay thousands of dollars for a premium slice of Over/Montgomery nodules with colorful variscite and crandallite.

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 the crystals are generally colorless to pale green and occur in nodules that are of sedimentary origin.  Today the Little Green Monster has been reclaimed and collecting is no longer available.

Above three photomicrographs have a width FOV ~9 mm.  The crystals of montgomeryite are embedded on a matrix of the feldspar microcline.

The best-known crystals found today are from a few mines in the Black Hills of South Dakota, especially the Tip Top Mine near Custer.  Here most crystals are some sort of a red to orange to salmon to pale yellow color and are associated with several other secondary phosphate minerals found in oxidized phosphate nodules occurring in granite pegmatites (associated with the Harney Peak Granite).  As noted in previous posts, Tom Loomis of DakotaMatrix.com owns the Tip Top and has located and preserved many of these rare phosphate minerals.

These three photomicrographs have a width FOV ~7mm.  Note the striations.

A section of the microcline matrix has a druse of really tiny (submillimeter) rhombohedral crystals of whitlockite (tricalcium phosphate; see Posting Dec. 10, 2018).  These crystals are difficult to observe except those whose faces reflect the light.  The terminated end of a montgomeryite crystal is visible along the right border. Width FOV ~7 mm.  

REFERENCES CITED

LARSEN, E. S., and SHANNON, E. V. (1930), The minerals of the phosphate nodules from near Fairfield, Utah: Am. Mineral., vol. 15, no. 8.

LARSEN, E. S. 3d, 1940, Overite and montgomeryite: two new minerals from Fairfield, Utah: The American Mineralogist, vol. 25, no. 3.

WILSON, Wendell E.,2018, Mineralogical Record Biographical archive: www.mineralogicalrecord.com.

Post Script:  I have hunted for crystals of overite for several years but have been unsuccessful in my pursuit.