Redefinition of beraunite, Fe<sup>3+</sup><sub>6</sub>(PO<sub>4</sub>)<sub>4</sub>O(OH)<sub>4</sub> ⋅ 6H<sub>2</sub>O, and discreditation of the name eleonorite: a re-investigation of type material from the Hrbek Mine (Czech Republic)
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Published:2022-04-12
Issue:2
Volume:34
Page:223-238
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ISSN:1617-4011
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Container-title:European Journal of Mineralogy
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language:en
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Short-container-title:Eur. J. Mineral.
Author:
Vrtiška LubošORCID, Tvrdý Jaromír, Plášil Jakub, Sejkora Jiří, Škoda Radek, Chukanov Nikita V., Massanek Andreas, Filip Jan, Dolníček Zdeněk, Veselovský František
Abstract
Abstract. Re-investigation of the type material of beraunite from
the Hrbek Mine, Svatá Dobrotivá, Czech Republic, proved the identity
of beraunite and eleonorite. Based on this study, the mineral eleonorite was
discredited, and the ideal formula of beraunite was redefined from
Fe2+Fe53+(PO4)4(OH)5 ⋅ 6H2O to
Fe63+(PO4)4O(OH)4 ⋅ 6H2O. Beraunite
from Hrbek Mine usually forms prismatic crystals flattened on
{100}; elongated along b axis, striated on
{100} || b, up to 0.2 × 0.5 × 3 mm, often in radial clusters up to 6 mm in size in
association with black goethite, olive-green to dark green dufrénite and
yellow to orange cacoxenite. Beraunite is hyacinth red, dark red, or
red-brown and has a light orange-red streak; crystals are translucent, with
a vitreous luster. The symmetry of the structure was found to be lower
(Cc) than reported in the past (C2/c); this has been proven by the crystal
structure refinement, Robs= 2.7 % for Cc and ∼ 8 %
for C2/m. Refined unit-cell parameters obtained from powder X-ray diffraction
data of the original material of Friedrich August Breithaupt are a= 20.653(2), b= 5.1433(6), c= 19.241(2) Å, β=93.560(9)∘, and V= 2039.9(2) Å3. Calculated density is 2.961 g cm−3. Beraunite is
optically biaxial (+), α= 1.768(2), β= 1.781(3),
γ>1.805, 2Vmeas= 69(4)∘,
and 2Vcalc is not possible to calculate. Dispersion of optical axes is
strong, r>v. The orientation is Y=b, X≈a, and Z≈c. Pleochroism is strong; Z (brown-red)
≫Y>X (both brownish yellow). The empirical formula of the
original beraunite sample calculated on the basis of P = 4
apfu is
(Fe5.763+Al0.15Zn0.01)5.92(PO4)4.00O0.99(OH)3.77 ⋅ 6H2O. The 57Fe Mössbauer spectrum of beraunite neotype
(National Museum, Prague) from type locality implies that all iron atoms in
beraunite structure are exclusively trivalent, located at the M site with
different next-nearest-neighbor configurations. There is no spectral
evidence for Fe2+ or iron in some impurities (e.g., limonite).
Funder
Ministerstvo Kultury Masarykova Univerzita Ministerstvo Školství, Mládeže a Tělovýchovy Ministry of Education and Science of the Russian Federation
Publisher
Copernicus GmbH
Subject
Pulmonary and Respiratory Medicine,Pediatrics, Perinatology and Child Health
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Cited by
3 articles.
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