Age and composition of oxalate-rich crusts in the northern territory, Australia

A. L. Watchman

Research output: Contribution to journalArticlepeer-review

80 Citations (Scopus)


The nature, origin and age of some thick multi-layered oxalate-rich crusts from quartz-rich rocks in Australia are presented, with a view to alerting restorers and conservators to their value in palaeo- environmental and rock art dating studies. Mineralogical and geochemical data, together with field observations and evidence from cross-section analysis, suggest that these deposits are formed naturally by chemical reaction of organic acids in rainwater acting on calcium-rich dust particles which have accreted on stable siliceous rock ledges and other sheltered surfaces. Carbon-14 dating of the oxalate mineral, whewellite, found in the surface crusts ranges from modern to 8800 years bp: evidence that the natural processes which form oxalate-rich surface deposits have been continuous for many thousands of years. Such dating of oxalate layers provides a means for establishing time-frames in which different prehistoric painting styles can be fixed; the method does not give a direct age for individual artistic motifs.

Original languageEnglish
Pages (from-to)24-32
Number of pages9
JournalStudies in Conservation
Issue number1
Publication statusPublished - 1991
Externally publishedYes


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