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Pohlite, a new lead iodate hydroxide chloride from Sierra Gorda, Chile

Published online by Cambridge University Press:  16 November 2022

Anthony R. Kampf Open the ORCID record for Anthony R. Kampf [Opens in a new window] ,
George E. Harlow  and
Chi Ma Open the ORCID record for Chi Ma [Opens in a new window]
Anthony R. Kampf*
Affiliation:
Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, CA 90007, USA
George E. Harlow
Affiliation:
Department of Earth and Planetary Sciences, American Museum of Natural History, 200 Central Park West, New York, NY 10024, USA
Chi Ma
Affiliation:
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
*
*Author for correspondence: Anthony R. Kampf, Email: [email protected]
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Abstract

The new mineral pohlite (IMA2022–043), Pb7(IO3)(OH)4Cl9, was found at La Compania mine, Sierra Gorda, Antofagasta Province, Antofagasta, Chile, where it occurs in cavities in an oxidised portion of a quartz vein in association with massive aragonite and anhydrite. Pohlite crystals are transparent, colourless to pale grey blades, up to 4 mm in length. The mineral has a white streak, adamantine lustre and is nonfluorescent. It is brittle with irregular, conchoidal fracture. The Mohs hardness is ~2½ and it has no cleavage. The calculated density is 5.838(2) g cm–3. Optically, the mineral is biaxial (+) with α < 2.01(est.), β = 2.02 (calc.), γ = 2.05 (calc.); 2V = 60(5)°; moderate r > v dispersion; orientation: Y ∧ a ≈ 20°, Z ∧ b ≈ 30°; and is nonpleochroic. The Raman spectrum exhibits bands consistent with IO3– and O–H. Electron microprobe analysis provided the empirical formula Pb6.74I1.00Cl9.29O6.71H4.23. The five strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 3.818(91)(023, 122, 1$\bar{2}$1), 3.674(85)($\bar{1}\bar{2}$1, $\bar{1}$22, 200, 104), 3.399(47)($\bar{2}$10, 210, $\bar{1}$04), 2.378(100)(302, 041, $\bar{2}$24) and 1.9943(45)(multiple). Pohlite is triclinic, P$\bar{1}$, a = 7.3366(5), b = 9.5130(9), c = 16.2434(15) Å, α = 81.592(7), β = 84.955(7), γ = 89.565(6)°, V = 1117.13(17) Å3 and Z = 2. The structure of pohlite (R1 = 0.0328 for 3394 I > 2σI) contains two types of clusters, a [Pb4(OH)3]5+ cluster formed by short Pb–O bonds and a [Pb3(OH)(IO3)]28+ ‘double cluster’ formed by short I–O bonds and short- to medium-length Pb–O bonds. Long Pb–Cl and I–Cl bonds link the clusters together in three dimensions.

Keywords

pohlitenew mineraliodatelone-pair electronsPb–(O,OH) clusterscrystal structureRaman spectroscopySierra GordaChile
Type
Article
Information
Mineralogical Magazine , Volume 87 , Issue 2 , April 2023 , pp. 171 - 177
Copyright
Copyright © The Author(s), 2022. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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Footnotes

Associate Editor: David Hibbs

References

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