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Guangyuanite, Pb3Cl3(Se4+O3)(OH), a new lead chloride selenite mineral from the El Dragón mine, Potosí, Bolivia

Published online by Cambridge University Press:  07 December 2023

Hexiong Yang*
Affiliation:
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA
Xiangping Gu
Affiliation:
School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, China
James A. McGlasson
Affiliation:
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA
Ronald B. Gibbs
Affiliation:
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA
Robert T. Downs
Affiliation:
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, AZ 85721-0077, USA
*
Corresponding author: Hexiong Yang; Email: hyang@arizona.edu
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Abstract

A new mineral species, guangyuanite, ideally Pb3Cl3(Se4+O3)(OH), was discovered from the El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia. It occurs as equant crystals. Associated minerals are Co-bearing krut'aite–penroseite, chalcomenite, schmiederite, olsacherite, phosgenite, anglesite, cerussite and franksousaite. Guangyuanite is pale yellow–brown in transmitted light, transparent with white streak and vitreous lustre. It is brittle and has a Mohs hardness of ~3. No parting or cleavage was observed. The calculated density is 7.63 g/cm3. An electron microprobe analysis yielded an empirical formula [based on 7 (O + Cl) atoms per formula unit] of Pb3.02Cl3.01(Se4+0.99O3)(OH), which can be simplified to Pb3Cl3(Se4+O3)(OH).

Guangyuanite is isostructural with synthetic Pb3Br3(Se4+O3)(OH). It is orthorhombic, with space group Pnma and unit-cell parameters a = 11.0003(5), b = 10.6460(5), c = 7.7902 Å, V = 912.31(6) Å3 and Z = 4. The crystal structure of guangyuanite contains two symmetrically-distinct Pb (Pb1 and Pb2) cations, with Pb1 coordinated by eight anions (4O + 4Cl) and Pb2 only by six anions (3O + 3Cl), forming a marked lopsided coordination typical of Pb2+ with a stereochemically active 6s2 lone electron pair. The Se4+ cation forms a typical [Se4+O3] trigonal pyramid. The crystal structure of guangyuanite can be described as consisting of layers of edge-sharing [Pb1O4Cl4] polyhedra parallel to (100). These layers are linked together by sharing polyhedral corners (Cl atoms), as well as [Pb2O3Cl3] and [Se4+O3] groups. Chemically, guangyuanite is one of six lead chloride selenite minerals reported thus far and closely related to orlandiite Pb3Cl4(Se4+O3)⋅H2O.

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Article
Copyright
Copyright © University of Arizona, 2023. Published by Cambridge University Press on behalf of The Mineralogical Society of the United Kingdom and Ireland
Figure 0

Table 1. List of lead-selenite-chloride minerals.

Figure 1

Figure 1. The specimen on which the new mineral guangyuanite, indicated by the blue arrow, was found. Specimen R210013.

Figure 2

Figure 2. A microscopic view of two yellow-brown guangyuanite crystals in a vug, specimen R210013.

Figure 3

Table 2. Chemical data (in wt.%) for guangyuanite.

Figure 4

Figure 3. Raman spectra of guangyuanite (R210013) and orlandiite (R100122).

Figure 5

Table 3. Powder X-ray diffraction data (d in Å, I in %) for guangyuanite.

Figure 6

Table 4. Crystallographic data and refinement statistics for guangyuanite and orlandiite.

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Table 5. Fractional atomic coordinates and equivalent/isotropic displacement parameters (Å2) for guangyuanite.

Figure 8

Table 6. Atomic displacement parameters (Å2) for guangyuanite.

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Table 7. Selected bond distances (Å) and angles (°) for guangyuanite and the Br-analogue.

Figure 10

Table 8. Bond-valence sums for guangyuanite.

Figure 11

Figure 4. Atomic coordinations in guangyuanite: (a) for [Pb1O4Cl4] polyhedron and (b) for [Pb2O3Cl3] and [Se4+O3] groups.

Figure 12

Figure 5. A layer of edge-sharing [Pb1O4Cl4] polyhedra (dark grey) in guangyuanite parallel to (100). Light grey, aqua, red, yellow, and green spheres represent Pb2, Cl, O, Se and H atoms, respectively. The unit cell is outlined. Drawn using XtalDraw software (Downs and Hall-Wallace, 2003).

Figure 13

Figure 6. Crystal structure of guangyuanite, showing the stacking of layers of edge-sharing [Pb1O4Cl4] polyhedra (dark grey) along the a-axis. The legends are the same as in Fig. 5.

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