Reports

Microbial Origin of Desert Varnish

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Science  11 Sep 1981:
Vol. 213, Issue 4513, pp. 1245-1247
DOI: 10.1126/science.213.4513.1245

Abstract

Scanning electron microscopy and energy dispersive x-ray analyses of desert varnish reveal that microorganisms concentrate ambient manganese that becomes greatly enhanced in brown to black varnish. Specific characteristics of desert varnish and of varnish bacteria support a microbial origin for manganese-rich films. Varnish microbes can be cultured and produce laboratory manganese films. Accordingly, natural desert varnish and also manganese-rich rock varnishes in nondesert environments appear to be a product of microbial activity.