title: Microbial origin of desert varnish.
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.
authors.forename: R I
authors.initials: RI
authors.lastname: Dorn
authors.forename: T M
authors.initials: TM
authors.lastname: Oberlander