Zanazziite

Composition

Zanazziite was recently analyzed with an ARL-SEMQ microprobe; the values were Durango apatite for P, Rockport fayalite for Mn, and Kakanui hornblende for all others. Zanazziite belongs to the roscherite-group. The roscherite-group nomenclature is based on the dominant cation in the Me-site; valid species include: Roscherite (Mn^2+), Zanazziite (Mg^2+) and Greifensteinite (Fe^2+).

Structure

Zanazziite belongs to the monoclinic space group C2/c. X-ray diffraction showed the strongest lines in Å, with intensities and indices: 9.50 (90) (110), 5.91 (100) (020), 3.16 (70) (330), 3.05 (50) (510), 2.766 (50) (240), 2.682 (40b) (600), 2.208 (40), 1.642 (50b). The biaxial orientation of the extinction angles: X=b; Z^a=3 degrees, angles: \alpha=1.606, \beta=1.610, \gamma=1.620, optical axis angle: 2V which was measured = 72 degrees and 2V which was calculated = 65 degrees. In X-ray scattering and diffraction models the data presents an approximation of the number of electrons in each atomic site, giving 17.3 e- in the M2 site and 64.8 e- in the M1 site.

The crystals in Zanazziite are prismatic to bladed, usually rough, barrel-shaped, with indices {100}, {110} and {001}. Cleavages are on {100} good, and {010} distinct.

Physical properties

Zanazziite is usually pale green and occasionally dark green. It is a 5 on the Mohs hardness scale. Optically biaxial +, ex = 1.606, 13 =1.610, "y = 1.620, 2V, = 72°(65° calc) X = b, Z:[100] 3° in obtuse 13; and the density = 2.76 measured, 2.77 calculated. Zanazziite has a vitreous luster, slightly pearly on the cleavage surfaces. Its cleavage is {100} good, {010} distinct. Zanazziite is nonfluorescent in longwave or shortwave ultraviolet light. Zanazziite also shares many physical properties with roscherite.

Geologic occurrence

The roscherite analog zanazziite was found in Lavar da Ilha deposits in Minas Gerais, Brazil. Zanazziite grows usually along the surface of quartz minerals. It occurs in pegmatite in beds of the Jequitinhonha river valley. The pegmatite consists of a wall zone rich in feldspar and muscovite, and a quartz core.

References

References

1. Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
2. [http://www.mindat.org/min-4385.html Zanazziite: Zanazziite on Mindat.org]
3. [http://www.webmineral.com/data/Zanazziite.shtml Zanazziite on Webmineral]
4. Atencio, D., Chukanov, N.V., Coutinho, J.M.V., Menezes Filho, L.A D., Dubinchuk, V.T. and Möckel, S.(2007) Ruifrancoite, a new Fe3+ -dominant monoclinic member of the roscherite group from Galilea, Minas Gerais, Brazil. The Canadian Mineralogist.,45, 1263–1273.
5. It is found in the crevices of Lavra da Ilha [[pegmatite]], near Taquaral, in northeastern [[Minas Gerais, Brazil]].Leavens, P.B., White, J.S., and Nelen, J.A.(1990) Zanazziite a new mineral from Minas Gerais, Brazil. The Mineralogical record 21, 413–417.
6. Rastsvetaeva, R.K., Barinova, A.V., Chukanov, N.V., and Pietraszko, A.(2004) Crystal structure of a magnesium-rich triclinic analogue of greifensteinite. Dok. Akad. Nauk. Russia., 398, 492–497.