Color-change processes of a plinian pumice and experimental constraints of color-change kinetics in air of an obsidian

Mihoko Moriizumi, Satoru Nakashima, Satoshi Okumura, Yuta Yamanoi

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Colors of plinian pumices were measured by spectrocolorimetry, and their quantitative color parameters in the L*ab* color space were determined. A series of heating experiments of obsidian was conducted to simulate the color-change processes of rhyolitic glasses. In these experiments, following three stages of color-change processes were observed. Stage I showed a rapid b* (yellowishness) increase associated with fast dehydration controlled by water diffusivity (Dwater). In stage II, a* (reddishness) increase was accompanied by Fe2+ decrease. Both a* increase and Fe2+ decrease can be simulated by a diffusion model. Obtained diffusivity Doxidation were about two orders of magnitude smaller than Dwater. The a*-value increase after the oxidation in stage III appeared to be quasi-linear with time, indicating the zeroth order reaction corresponding to the formation of hematite-like structures in rhyolitic glasses. The diffusion-limited a* increase model in stage II was applied to a natural plinian pumice fall unit to evaluate time periods of color-change processes through oxidation by air of fragmented rhyolitic materials.

Original languageEnglish
Pages (from-to)1-13
Number of pages13
JournalBulletin of Volcanology
Volume71
Issue number1
DOIs
Publication statusPublished - 2009 Jan 1

Keywords

  • Color-change process
  • Iron
  • Obsidian
  • Oxidation
  • Plinian eruption
  • Pumice
  • Spectrocolorimetry

ASJC Scopus subject areas

  • Geochemistry and Petrology

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