IMA 2003-039 = museumite

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Marco E. Ciriotti
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IMA 2003-039 = museumite

Messaggio da Marco E. Ciriotti » lun 01 nov, 2004 13:58

A IMA 2003-039, una nuova fase relazionata a buckhornite e nagyágite, rinvenuta su un campione di Sacarîmb, Romania, giacente nel museo della capitale toscana, è stato dato il nome di museumite.
Qui di seguito la referenza completa e l'abstract della descrizione della specie:

• Bindi, L. & Cipriani, C. (2004): Museumite, Pb5AuSbTe2S12, a new mineral from the gold-telluride deposit of Sacarîmb, Metaliferi Mountains, western Romania. European Journal of Mineralogy, 16, 834-837.

Abstract: Museumite, ideally Pb5AuSbTe2 S12, is a newly identified mineral from the gold-telluride deposit of Sacarîmb, Metaliferi Mountains, western Romania. The mineral occurs as anhedral to subhedral grains up to 300μm in cavities and vugs of large nagyágite crystals and it does not show any inclusion or intergrowth of other minerals. The associated minerals are nagyágite, hessite, sylvanite, petzite and coloradoite, whereas the gangue minerals are calcite and quartz. Museumite is dark silver-grey in colour and shows a grey-black streak. It has a perfect {001} cleavage, the fracture is hackly and the Vickers hardness (VHN15) is 42 kg/mm2. Museumite is greyish white in reflected light, with very low bireflectance and pleochroism. With crossed polars it shows distinct anisotropism, similar to nagyágite, but slightly stronger. Internal reflections are absent. Reflectance percentages for Rmin and Rmax are 38.4, 40.3 (471.1 nm), 38.1, 40.1 (548.3 nm), 37.5, 39.4 (586.6 nm), and 35.9, 38.0 (652.3 nm), respectively. Museumite is monoclinic, space group P21 or P21/m, with the following unit-cell parameters: a = 4.361(2) Å, b = 6.618(3) Å, c = 20.858(9) Å, β = 92.71(5)°, V = 601.3(5) Å3. The strongest five powder-diffraction lines [d in Å (I/I0 ) (hkl)] are: 4.80 (52) (013); 3.56 (100) (111); 3.47 (58) (112); 2.99 (50) (023); 2.56 (41) (116). The average of 25 electron microprobe analyses gave Pb 52.0(4), Au 10.7(1), Sb 6.2(2), Te 11.7(2), S 19.4(2), total 100.0 wt. %, corresponding, on the basis of total atoms = 21, to Pb5.00Au1.08Sb1.01Te1.83S12.08.
Marco E. Ciriotti

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