Analysis of rock varnish from the mojave desert by handheld laser-induced breakdown spectroscopy

Russell S. Harmon, Daria Khashchevskaya, Michelle Morency, Lewis A. Owen, Morgan Jennings, Jeffrey R. Knott, Jason M. Dortch

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Laser-induced breakdown spectroscopy (LIBS) is a form of optical emission spectroscopy that can be used for the rapid analysis of geological materials in the field under ambient environmental conditions. We describe here the innovative use of handheld LIBS for the in situ analysis of rock varnish. This thinly laminated and compositionally complex veneer forms slowly over time on rock surfaces in dryland regions and is particularly abundant across the Mojave Desert climatic region of east-central California (USA). Following the depth profiling examination of a varnished clast from colluvial gravel in Death Valley in the laboratory, our in situ analysis of rock varnish and visually similar coatings on rock surfaces was undertaken in the Owens and Deep Spring valleys in two contexts, element detection/identification and microchemical mapping. Emission peaks were recognized in the LIBS spectra for the nine elements most abundant in rock varnish—Mn, Fe, Si, Al, Na, Mg, K, Ca and Ba, as well as for H, Li, C, O, Ti, V, Sr and Rb. Focused follow-up laboratory and field studies will help understand rock varnish formation and its utility for weathering and chronological studies.

Original languageEnglish
Article number5200
Issue number17
StatePublished - Sep 1 2021

Bibliographical note

Funding Information:
for the purchase of the Z-300 LIBS analyzer was provided by North Carolina State University. Support for fieldwork and salary was provided to L.A.O. under the university startup funding. J.R.K. was supported by National Science Foundation grant EAR-1516593.We extend our sincere appreciation to Jack Hansen (SciAps, Inc.) for the excellent infield training on the Z-300 handheld LIBS analyzer.

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.


  • Desert pavement
  • Geochemical fingerprinting
  • Laser-induced breakdown spectroscopy (LIBS)
  • Microchemical mapping
  • Rock varnish

ASJC Scopus subject areas

  • Analytical Chemistry
  • Chemistry (miscellaneous)
  • Molecular Medicine
  • Pharmaceutical Science
  • Drug Discovery
  • Physical and Theoretical Chemistry
  • Organic Chemistry


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