Richard M. Kettler
Date of this Version
A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science
Major: Earth and Atmospheric Science
Under the supervision of Professor Richard M. Kettler
Lincoln, Nebraska, December 2023
In the western and southwestern United States, the term wonderstone is used to describe volcanic, volcaniclastic, and sedimentary rocks with variegated banding produced by iron oxide mineralization or staining. This iron oxide mineralization is typically described as Liesegang banding. In this paper I will (1) test if the banding in wonderstone follows the spacing and width laws characteristic of Liesegang, (2) identify the source of iron that ultimately precipitated in the bands, and (3) examine the role that microbes played in the formation of the mineralization in these rocks. I conclude that the iron oxide mineralization is not Liesegang banding. Only three of 51 wonderstone samples examined comply with the Jablczynski spacing law and width law characteristic of Liesegang. Iron in the banding was derived from ferrous silicates in the rock. Both petrographic and Energy Dispersive (X-Ray) Spectroscopy (EDS) data provide evidence for reductive dissolution of biotite and hornblende within wonderstone, Tertiary sediment, and rhyolite. Hornblende is absent from the wonderstone, whereas biotite is altered within the stained and iron oxide mineralized zones. Both minerals are absent from the bleached zones. The absence of hornblende and occurrence of altered biotite with iron staining around the edges of the mineral within the stained and mineralized zones is evidence that these two minerals were the original iron source. Morphotypes similar to iron-oxidizing bacteria were observed within wonderstone. I interpret that reducing anoxic waters saturated the wonderstone precursor causing iron to gradually leach out of the biotite and hornblende present within those rocks. Later oxidizing fluids and oxidizing bacteria invaded the rocks and facilitated the precipitation of the free aqueous ferrous iron to produce the iron oxide mineralization.