Lead in zircon at the atomic scale

Masashi Kogawa, E. Bruce Watson, Rodney C. Ewing, Satoshi Utsunomiya

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Lead-doped zircon crystals, which were synthesized under three different conditions (Watson et al. 1997): dry at 1430 °C at atmospheric pressure without P 2 O 5 ; wet at 900 °C at 1.5 GPa in the presence of P 2 O 5 ; and wet at 800 °C at 1.0 GPa without P 2 O 5 , have been investigated to understand the mechanisms of Pb incorporation into zircon at the sub-micrometer scale, using various electron microscopy techniques including high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Four different mechanisms in which Pb may be incorporated into zircon have been identified. In the P-free synthesis, Pb-oxide hydrate particles, 50-200 nm in size, are embedded in zircon. Each Pb-particle is associated with a single vesicle, ∼50 nm. Lead in the zircon structure is possibly incorporated under the detection limit value of energy-dispersive X-ray analysis (EDX) by means of: (1) Zr 4+ = Pb 2+ + 2H + at less than -0.1 wt%. In the system with P, Pb-phases occur in three different forms: Pb-rich domains concentrated along cleavage planes or grain boundaries without any evident crystal form; numerous Pb-phosphate particles, as large as 100 nm, embedded heterogeneously in the zircon crystal; and homogeneous distribution of Pb in the zircon structure at less than -1 wt% as determined by EDX. These results suggest that charge balance is maintained by the xenotime-type coupled substitution: (2) Zr 4+ + 2Si 4+ = Pb 2+ + 2P 5+ with a possible minor contribution from mechanism 1. The apparent solubility limit of Pb, <1 wt%, is constrained mainly by the xenotime-type coupled substitution mechanism, which is probably due to increasing strain at higher Pb-concentrations. The presence of Pb 2+ in natural zircon is consistent with the low-level Pb allowed by substitution mechanism 2, with only a minor contribution from substitution mechanism 1, the latter of which causes distortion in the local structure.

Original languageEnglish
Pages (from-to)1094-1102
Number of pages9
JournalAmerican Mineralogist
Volume97
Issue number7
DOIs
Publication statusPublished - Jul 1 2012

Fingerprint

zircon
substitutes
substitution
Substitution reactions
xenotime
Energy dispersive X ray analysis
crystal
Crystals
X-ray spectroscopy
transmission electron microscopy
doped crystals
hydrates
crystals
Lead
micrometers
cleavage
electron microscopy
atmospheric pressure
phosphates
x rays

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Lead in zircon at the atomic scale. / Kogawa, Masashi; Watson, E. Bruce; Ewing, Rodney C.; Utsunomiya, Satoshi.

In: American Mineralogist, Vol. 97, No. 7, 01.07.2012, p. 1094-1102.

Research output: Contribution to journalArticle

Kogawa, M, Watson, EB, Ewing, RC & Utsunomiya, S 2012, 'Lead in zircon at the atomic scale', American Mineralogist, vol. 97, no. 7, pp. 1094-1102. https://doi.org/10.2138/am.2012.3993
Kogawa, Masashi ; Watson, E. Bruce ; Ewing, Rodney C. ; Utsunomiya, Satoshi. / Lead in zircon at the atomic scale. In: American Mineralogist. 2012 ; Vol. 97, No. 7. pp. 1094-1102.
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