This group of goethite–quartz boulders may have formed from a hydrothermal seam or vent, where silica and sulfur-rich fluids precipitated quartz and pyrite. As pyrite oxidizes, it typically forms sulfuric acid, which accelerates iron oxidation, in this case forming goethite. As the surrounding blocky shale erodes, the more resistant goethite-quartz boulders remain – a common sight in the Flinders Ranges.
