Spectroscopy, mineralogy, and morphology of a jarosite-bearing landmark butte within the Jurassic Navajo Sandstone

The distinctive topography of a butte located in the Jurassic Navajo Sandstone of Utah has made it a landmark within the region. This butte, "Mollies Nipple" ("Mollie's"), is within the Grand Staircase - Escalante National Monument located in south-central Utah. It rises approximately ∼200 meters above its base. This research seeks to answer the question as to how the current morphology of "Mollies" came to be such a distinct and isolated butte in this area. Spectral analysis shows the presence of a mineral not commonly found in this area, jarosite, and this erosion-resistant jarosite cement is assumed to control Mollie's morphology. Three hypotheses are proposed based on known mechanisms of jarosite formation to explain the jarosite cement: the jarosite formed in an acid saline environment, a hydrothermal environment, or as the result of sulfide weathering. Spectral analysis using satellite, aerial, and field sample data is used to identify the mineralogy at the butte and relate it to the butte's morphology. Additional analytical techniques, including x-ray diffraction, scanning electron microscopy, petrography, trace element geochemistry, and reflectance spectroscopy of experimental mineral mixtures were used to support the spectral analysis and provide additional constraints on the conditions of jarosite formation. Results indicate that "Mollie's" was shaped as a result of erosion-resistant jarosite cement likely formed by sulfide (pyrite) weathering that preferentially precipitated jarosite along local faults.