LAUEITE; ANOTHER PHOSPHATE FROM THE BLACK HILLS & NEW HAMPSHIRE

 

I recently was able to purchase two phosphate micros mounted by Art Smith. One was labeled laueite & rockbridgeite, Big Chief Mine, Glendale, South Dakota, 1977, while the other shows laueite, Palermo #1 Mine, North Groton, Grafton County, New Hampshire, with a date of perhaps 1997.  Both of these mines are famous for their micro secondary phosphate minerals.

The Big Chief Mine (Glendale Mining District) is located not far from the tourist town of Keystone in Pennington County. The Big Chief was never a large producer, in the late 1800s, of primary feldspar and mica and secondary beryl hacked out of a small cut and a short drift in a couple of Proterozoic (Precambrian) zoned pegmatites. However, this small mine has yielded 73 different minerals and varieties including the phosphates olmsteadite, perloffite, and metavivianite that call the Big Chief their Type Locality (MinDat). Recently a beryllophosphate [Ba[Be₂P₂O₈]-H₂O] was described and the Mine became the Type Locality of mineral #4 named loomisite (Yang and others, 2022).  —see BLOG Posting July 29, 2022 https://csmsgeologypost.blogspot.com/2022/07/whitemoreite-black-hills-phosphate.html  

The second laueite specimen was collected from the Palermo #1 Mine. The Graton Pegmatite Field, with the Palermo Pegmatites, is located in the Acadian Orogenic Belt, a tectonic area that represents the Devonian (~420Ma --~360 Ma) uplift of mountains in the northern section of the Appalachian Orogen, around southern Virginia to Newfoundland. This uplift was the result of plate movement as a microcontinent named Avalonia (parts of Europe) was banging against Laurentia (proto North America), and being accreted (the terrane was sticking to Laurentia) while the proto Atlantic Ocean was being subducted under the Laurentian continental plate. Of course, the orogenic event was much more complex that this explanation! What we also know is that the active tectonic zone supplied magmatic plutons, volcanos, hydrothermal fluids, and lots of heat for metamorphic transformation of preexisting rocks. One primary mineral that was subjected to heat and fluids was most likely the lithium iron phosphate, triphylite.

Laueite [Mn⁺⁺Fe⁺⁺⁺₂(PO₄)₂(OH)₂-8H₂O], a brightly colored mineral compared to its precursor triphylite, displays colors from honey to amber, to various shades of orange, and yellow. Crystals are tiny rhombs or wedges with lengths usually less than 2 mm, have a vitreous to resinous luster, and are transparent to translucent.

Laueite is not common from pegmatite mines in the Black Hills with MinDat listing a half dozen localities (including the Big Chief) and only three photos shown, all from the Tip Top. Roberts and Rapp (1965) stated “yellowish-orange crystals of laueite up to 1/16 inch in size occur in vugs intimately associated with strunzite and altered triphylite at the Big Chief Mine.”  In 1974 Roberts, Rapp, and Weber noted that laueite occurs on rockbridgeite …at several pegmatites in the Keystone and Custer Districts…especially at the Tip Top…and Big Chief.” 

Laueite crystals from vugs in rockbridgeite and collected from the the Big Chief Mine.  Bottom photomicrograph length of crystals ~.6 mm. Top cluster maybe ~.3 mm.  Note terminations.  

The Palermo No. 1 Mine has produced a substantial number of laueite specimens. The micromount in my collection has two tiny vugs: 1) a 2 mm long void filled with a jackstraw arrangement of .1 to .2 mm, small (very small), translucent, amber crystals; some with rhomb terminations; and 2) the adjacent second vug has larger (~.9 mm), amber to gold, elongated, striated rhomb crystals. Occasional needle-like strunzite (hydrated manganese iron phosphate) also show up in bottom two photos.. 

 

This has been an interesting project for a number of reasons, not the least of which was the size of the crystals. Photography was difficult and my photomicrographs are the best that I could achieve. The pegmatites of the Black Hills and New England have produced an amazing number and variety of minerals, many of them being ”micro crystals.”  I hope to have access to additional micromounts in the future.

REFERENCES CITED

Roberts, W.L. and G. Rapp, Jr., 1965, Mineralogy of the Black Hills: South Dakota School of Mines and Technology, Bulletin Number 18.

Roberts, W.L., G. Rapp, Jr., and J. Weber, 1974, Encyclopedia of Minerals: Von Nostrand Reinhold Company, New York.

Yang, H., Gu, X., Gibbs, R. B., and Scott, M. M., 2022, Loomisite, IMA 2022-003, in: CNMNC Newsletter 67. European Journal of Mineralogy: 34.