Baking black opal in the desert sun: The importance of silica in desert varnish: COMMENT AND REPLY: COMMENT

Abstract

[Perry et al. (2006)][1] contribute a fourth alternative, of silica binding, to three prior hypotheses of varnish formation: 1) abiotic Mn-Fe enhancement (e.g., [Engel and Sharp, 1958][2]); 2) biotic Mn-Fe enhancement (e.g., [Dorn and Oberlander, 1982][3]; [Allen et al., 2004][4]); and 3) a