The MP2 Research Group Abstracts

New Data on Roscherite-Group Minerals from New England and South Dakota, USA and Brazil James W. Nizamoff 1, Alexander U. Falster 1, Carl A. Francis 2, D. E. Lange 2, L. Menezes 3, William B. Simmons 1 1 MP2 Research Group, Dept. of Earth and Environmental Sciences, University of New Orleans, New Orleans, LA 70148 2 Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138 3 R. Esmeralda, 536, Belo Horizonte, 30410 080, Brazil

The minerals of the roscherite group consists of three species with a general formula of Ca2Be4Me5(PO4)6(OH)4 • 6 H2O, where the Me-site may contain Fe2+, Fe3+, Mn2+, Mg, or Al (Atencio 2002, Rastvetaeva et al., 2002). However, some uncertainty exists regarding the exact structural formula and the role of trivalent cations in the roscherite group. Currently, roscherite-group nomenclature is based on the dominant cation in the Me-site, valid species include: Roscherite (Mn2+), Zanazziite (Mg2+) and Greifensteinite (Fe2+).

	Figure 1 - A recent microprobe study of several roscherite-group minerals from New England and South Dakota, USA, revealed interesting results: backscattered electron imaging and microprobe analyses show striking compositional zoning in many of the samples.
		Figure 1: Ternary plot of the three major divalent cations in the Me-site (Mg, Mn, and Fe) for roscherite-group minerals from the U.S.
	Figure 2 - A recent microprobe study of several roscherite-group minerals from Brazil, SA, revealed interesting results: backscattered electron imaging and microprobe analyses show striking compositional zoning in many of the samples.
		Figure 2: Ternary plot of the three major divalent cations in the Me-site (Mg, Mn, and Fe) for roscherite-group minerals from Minas Gerais, Brazil.

	Specimens from the Estes quarry, West Baldwin, Maine, exhibit a considerable range in composition from roscherite to greifensteinite and are associated with beryllonite, childrenite-eosphorite and muscovite. Samples from the Martin prospect, Newry, Maine are confirmed as zanazziite. Martin prospect zanazziite displays little compositional variation and occurs with hydroxylherderite and fluorapatite. The Black Mountain, Rumford, Maine samples yield compositions ranging from greifensteinite to roscherite with virtually no Mg component. Specimens from the Palermo #1 mine, North Groton, New Hampshire historically labeled as roscherite display a range in composition from greifensteinite to zanazziite and are associated with childrenite-eosphorite, bjarebyite and palermoite. Samples from the Tip Top pegmatite, near Custer, South Dakota vary in composition from roscherite to greifensteinite. Tip Top roscherite contains the highest Mn found in this study and is associated with tiptopite, englishite and montgomeryite.
	In Brazil, compositions of roscherite-group minerals from the Galiléia district range from greifensteinite to zanazziite to roscherite and are associated with beryllonite, moraesite, childrenite-eosphorite and ushkovite. In comparison, samples from the Sapucaia and Lavra do Criminoso pegmatites exhibit relatively little compositional variation and fall entirely within the greifensteinite field. Roscherite-group minerals from the Jenipapo pegmatite are dominantly zanazziite with a significant greifensteinite component and are associated with kosnarite, ushkovite and albite. Linópolis samples vary between greifensteinite and zanazziite and occur with childrenite-eosphorite, gormanite and albite.
	The data show extensive solid solution between greifensteinite and roscherite and between greifensteinite and zanazziite, but very limited solid solution between roscherite and zanazziite. Additional work is required to formulate an explanation regarding the paucity of roscherite-zanazziite solid solution observed in these pegmatites.

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Literature/References Cited: 1] Atencio, D. (2002) "Roscherite-group minerals from Brazil" Abstracts of the 18th General Meeting of the International Mineralogical Association, 18. 2] Rastsvetaeva, R.K., O.A. Gurbanova, and N.V. Chukanov (2002) "Crystal structure of greifensteinite Ca2Be4(Fe2+,Mn)5(PO4)6(OH)4 · 6 H2O" Doklady Chemistry, 383 (1-3), 78-81 (in English).

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