Publication Date:
2015-08-22
Description:
Ferribushmakinite (IMA2014-055), Pb 2 Fe 3+ (PO 4 )(VO 4 )(OH), the Fe 3+ analogue of bushmakinite, is a new mineral from the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, USA, where it occurs as a low-temperature secondary mineral in association with plumbogummite, mottramite, Br-rich chlorargyrite and baryte on massive quartz. Ferribushmakinite forms yellow slightly flattened prisms up to 0.2 mm long growing in X and sixling twins. The streak is pale yellow. Crystals are translucent and have adamantine lustre. The Mohs hardness is ~2, the tenacity is brittle, the fracture is irregular to splintery and crystals exhibit one or two fair cleavages in the [010] zone. The calculated density is 6.154 g/cm 3 . Electron microprobe analyses provided: PbO 63.69, CaO 0.07, CuO 1.11, Fe 2 O 3 7.63, Al 2 O 3 1.63, V 2 O 5 12.65, As 2 O 5 3.09, P 2 O 5 8.63, H 2 O 1.50 (structure), total 100.00 wt.% (normalized). The empirical formula (based on nine O a.p.f.u.) is: (Pb 1.99 Ca 0.01 ) 2.00 (Fe 0.66 Al 0.22 Cu 0.10 ) 0.98 (V 0.97 P 0.85 As 0.19 ) 2.01 O 7.84 (OH) 1.16 . Ferribushmakinite is monoclinic, P 2 1 / m, a = 7.7719(10), b = 5.9060(7), c = 8.7929(12) Å, β = 111.604(8)°, V = 375.24(9) Å 3 and Z = 2. The eight strongest lines in the powder X-ray diffraction pattern are [ d obs in Å ( I )( hkl )]: 4.794(46)(011); 3.245(84)(2I11); 2.947(100)(020,2I12,1I03); 2.743(49)(112); 2.288(30)(220); 1.8532(27)(3I14,4I03); 1.8084(27)(multiple); and 1.7204(28)(312,114,321). Ferribushmakinite is a member of the brackebuschite supergroup. Its structure ( R 1 = 3.83% for 577 F o 〉 4 F ) differs from that of bushmakinite only in the dominance of Fe 3+ over Al in the octahedral site.
Print ISSN:
0026-461X
Electronic ISSN:
1471-8022
Topics:
Geosciences
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