If you are a fan of the great outdoors, you
have probably noticed that you feel happier beyond the confines of your home.
This little tidbit of wisdom is not my original writing; however, I suspect all rockhounds probably have “thought this” and just neglected to place it on paper. Instead, we waited for Michael Bassey Johnson to publish such in Song of a Nature Lover. He also noted that “it is scientifically proven that flowers make you feel better? And even just looking at pictures of nature lowers your stress level?”
That is one reason that my office is crowded,
and I mean crowded, with paintings, sculptures, do dads, and photographs of “nature.” In fact, my wall time piece sounds like a Minnesota loon every hour. No cuckoo for me.
A print by Terry Redlin: Pure Contentment. Was I there, or was this a dream?
From my desk chair I look directly at seven framed prints by South Dakotan Terry Redlin. They all remind me of past experiences, both real and in my dreams. I look to them for inspiration in releasing words and thoughts from the back recesses of my mind. For example, how do specimens of roscherite (a tiny secondary phosphate) from the Tip Top Mine in the Black Hills compare with specimens from the mines in Maine? I need to check that out—and off I go. Yea, I know my mind works in mysterious ways and I am again reminded of Michael Bassey Johnson: “I saw a tree dancing in the wind, and it said to me, I’m not doing this to entertain you, but to remind you of what life is — a dance in the wind!” That sort of sums it up for my great life thus far, a dance in the wind!
Front Range, Colorado: A dance in the wind.
So, these thoughts bring me back to roscherite, a beryllium phosphate with additional calcium and manganese cations: Ca2Mn3Be4(PO4)(OH)4-6H2O. I am most familiar with roscherite from the Tip Top Mine in Custer Counter, South Dakota. This former tin (cassiterite), mica, lithium, feldspar, beryl (beryllium) mine is the Type Locality for something like 12 colorful phosphate minerals and tens of others are mostly hidden away in vugs and fractures; most are microscopic, but all seem to have beautiful crystals. The pegmatite at the Tip Top, like most others in the area, is related to the 1.7 Ga Harney Peak Granite that forms the core of the Black Hills (Lufkin and others, 2009). Tom Loomis, he of Dakota Matrix fame, is the mine owner.
Roscherite usually appears as tiny rounded spherical grains with a variety of colors possible—red, orange, brown, brownish yellow, yellowish green. They have a measured hardness of ~4.5 (Mohs), sort of a greasy to resinous luster, and leave a white streak. Tom Loomis at Dakota Matrix has stated that the Roscherites at Tip Top are crystallized in a range of colors and the lilac colored crystals may be Zanazziite, the Mg member. My specimen from the Tip Top has tens of tiny greenish to yellowish spheres clustered together on a quartz matrix. They are very pretty crystals, but small.
I recently was able to purchase a couple of micromounts (roscherites) put together by Art Smith: one from the P.Y. Estes Quarry, West Baldwin, Cumberland County, Maine, and the other from the Black Mountain Quarry, Rumford, Oxford County, Maine. Both specimens were collected by Gene Bearss, a noted collector of minerals from the mines of New England, and a member of the Micromounters Hall of Fame.
The Estes Quarry is an aggregate excavation located in southwestern Maine and has been extensively studied by Thompson and others (2000). They described the exposed granite pegmatite as alternating layers of fine-grained pegmatite, coarse -grained pegmatite, and sugary aplite. The rock forming minerals are albite, microcline, muscovite, and quartz. MinDat lists 63 valid minerals known from the quarry including a very large suite of accessory minerals and secondary phosphates associated with triphylite. Among the more common accessory minerals are beryl, columbite, and columbite; however, the quarry is best known for its assemblage of rare secondary phosphate minerals.
Thompson and others (2000) described the beryllium phosphate roscherite as microcrystals with a wide variety of habits: single, composite, bow-ties, fans, botryoids, and drusy encrustations. The crystals are a variety of colors ranging from colorless and white to many different shades of green, yellow, and amber. Roscherite is one of the latest minerals to crystalize in the pegmatite paragenesis (sequence in which the minerals form).
However, since Thompson and others (2000) published their seminal paper, much has been discovered in the roscherite arena. It seems that in the first decade of this century several studies were able to identify new roscherite-like minerals with strings of beryllium and phosphate tetrahedra anions with different amounts and kinds of the cations Ca, Fe++, Fe+++, Mn, Zn, Mg. MinDat described these Roscherite Group minerals as “complex monoclinic or triclinic metal-beryllium phosphate (with one arsenate).” These Group minerals (eight of them) are often tough to visually identify (at least to an ole plugger like me).
So, what do these studies mean to roscherite identifications form the Estes Quarry? Well, there is a good answer for that question if you can locate a copy of the abstracts for the 30th Rochester Mineralogical Symposium and zero in on a paper by Nizamoff and others (2003): specimens from the Estes quarry…exhibit a considerable range in composition from roscherite to greifensteinite and are associated with beryllonite, childrenite-eosphorite, and muscovite. MinDat, in its list of minerals for the Estes Quarry, noted that all roscherite-like specimens should now be listed as greifensteinite, a group mineral that is isostructural with roscherite—same crystal structure but a different chemical composition. In this case ferrous iron with a +2 oxidation state has substituted for manganese [Ca2Fe5Be4(PO4)(OH)4-6H2O]. Again, visually the two minerals look similar and have fairly identical properities. One may need a microprobe to distinguish between the two!
My second micromount was collected from the Black Mountain Quarry, Rumford, Oxford County, Maine, also by Gene Bearss, with identified roscherite. The pegmatites near Rumford are part of the Oxford County pegmatite field and “are situated in the Central Maine Belt, a belt of meta-sedimentary rocks that were deposited in the Late Ordovician, Silurian, and earliest Devonian periods. These rocks originated as marine sediments deposited in a deep-water basin, the Central Maine Basin, immediately before and during the Acadian orogeny (Bradley et al. 2000). Deformation and metamorphism of the lithified sediments took place during the Acadian, Neoacadian, and Alleghenian orogenies” [Devonian through Permian Periods; ~375 Ma-- 260 Ma] (Falster and others, 2019).
The Black Mountain pegmatite is well-known for opaque pink rubellite variety of elbaite tourmaline fans in lepidolite and quartz. MinDat lists 57 valid minerals known from the pegmatite including one Type, kosnarite. This phosphate was named to honor Rich Kosnar, a Colorado Mineral Dealer (Mineral Classics).
Nizamoff and others (2004) stated, “the Black Mountain, Rumford Maine, samples yield compositions ranging from greifensteinite to roscherite with virtually no Mg composition [zanazziite].” MinDat has two photos of greifensteinite only but does list roscherite as occurring in the quarry. I cannot locate the paper that made the decision about greifensteinite occurring as the dominant Roscherite Group mineral. Thompson (1998) in his guide to Maine minerals stated that the localities Buckfield, Newry, Paris, and Rumford (Black Mountain) had yielded Roscherite Group specimens. At that time, I believe the term Roscherite Group was informal and referred to three minerals: roscherite, the manganese analog, greifensteinite the iron analog, and zanazziite, the magnesium analog.
King (1988), in his studies of the nearby Dutton Pegmatite, noted a series of alterations and replacement in the parent rock. The sodium beryllium phosphate mineral beryllonite was attacked by calcium-bearing fluids with the sequence of alteration as: beryllonite, hydroxylherderite, rhodochrosite, eosphorite, and manganese-rich? roscherite.
The specimen in my collection has exceedingly tiny crystals (submillimeter) of what I presume is greifensteinite scattered on albite feldspar.
I suppose this little exercise has taught me that: 1) unless I have access to electronic gizmos it might be best to refer any unknown roscherite-like specimens to Roscherite Group; 2) one ole plugger can have a great time learning about minerals and the unknown; and 3) "A life spent in nature is a life well lived” M B. Johnson.
REFERENCES CITED
Bradley, D. C., R. D. Tucker, D. Lux, A. G. Harris, and D. C. McGregor, 2000, Migration of the Acadian orogen and Foreland Basin across the northern Appalachians: U.S. Geological Survey Professional Paper 1615.
Falster, A.U., W.B. Simmons, K. L. Webber, D.A. Dallaire, J. W. Nizamoff, and R.A. Sprague, 2019, The Emmons Pegmatite, Greenwood, Oxford County, Maine: Rocks & Minerals vol. 94, no. 6.
King, V.T., 1988, Beryllium phosphate alteration at a Newry, Maine, pegmatite: Contributed Papers in Specimen Mineralogy: 14th Rochester Academy of Science Mineralogical Symposium, Rocks & Minerals, vol. 63, no. 2.
Lufkin, J.L., J.A. Redden, A. Lisenbee, and T. Loomis, 2009, Guidebook to the Geology of the Black Hills:Golden Publishers, Golden, CO.
Nizamoff, J.W., A.U. Falster, C.A. Francis, D.B. Lange, L. Menezes, and W.B. Simmons, 2004, New data on Roscherite -Group minerals from New England, South Dakota, and Brazil: Contributed Papers in Specimen Mineralogy: 30th Rochester Academy of Science Mineralogical Symposium, Rocks & Minerals, vol. 79, no. 5.
Thompson, W.B., 1998, A collector’s guide to Maine mineral localities, 3rd Ed., Maine Geological Survey, Natural Resources Information and Mapping Center, Dept. of Conservation.
No comments:
Post a Comment