Plumboagardite, a new mineral of the mixite group from an occurrence in the Southern Black Forest, Germany

Authors: Walenta, Kurt; Theye, Thomas

Source: Neues Jahrbuch für Mineralogie - Abhandlungen, Volume 181, Number 3, June 2005 , pp. 219-222(4)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

Plumboagardite occurs among the secondary minerals of the mine Aitern Süd in the Southern Black Forest, Baden-Württemberg, Germany, in association with quartz, fluorite, chrysocolla and limonite.

It forms spherulitic aggregates of radial fibrous structure on chrysocolla composed of acicular crystals elongated [0001] and reaching 0,05 mm in length. Colour green, streak greenish, lustre vitreous, no distinct cleavage, hardness 3, density (calc.) 3.741g/cm³. Optical properties: n 1.726 (5), n 1.805 (5), uniaxial (⁺).

Unit-cell dimensions of the hexagonal mineral: a 13.77(2), c 5.94 (1), Z = 2, space group P6₃/m. Strongest lines of the powder pattern: 12.01 (10) 1010, 4.51 (6) 2130, 1121, 3.60 (8), 2131, 2.98 (6) 4040, 2241, 0002, 2.49 (7) 3251, 3142. Chemical composition (wt.%): PbO 8.99, La₂O₃ 1.91, Nd₂O₃ 1.17, Ce₂O₃ 0.96, Sm₂O₃ 0.20, Pr₂O₃ 0.19, Gd₂O₃ 0,17, Dy₂O₃ 0.10, Y₂O₃ 0.96, CaO 1.44, CuO 40.49, Fe₂O₃ 1.54, As₂O₅ 29.74, P₂O₅ 0.30, SiO₂ 1.46, H₂O (by difference) 10.38, total 100.00%. The empirical formula – based on 12 O + 6 OH structural anions – is: [Pb_0.44(La_0.13Y_0.09Nd_0.08Ce_0.06Pr_0.01Sm_0.01Gd_0.01Dy_0.01)_{REE = 0.40}Ca_0.28]_{= 1.12}(Cu_5.59Fe_0.21)_{= 5.80}(As_2.84Si_0.27P_0.05)_{= 3.16}O₁₂(OH)₆ · 3.33H₂O simplified (Pb,REE,Ca)Cu₆(AsO₄)₃(OH)₆ · 3H₂O. The mineral is easily soluble in dilute HCl and HNO₃.

Keywords: MIXITE GROUP; PARAGENESIS; OPTICAL PROPERTIES; CRYSTALLOGRAPHIC DATA; POWDER PATTERN; MINE AITERN SUD (SOUTHERN BLACK FOREST BADEN-WURTT

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0077-7757/2005/0019

Publication date: 2005-06-01

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