^1,2Toshimori Sekine,²Tsubasa Tobase,³Youjun Zhang,⁴Ginga Kitahara,⁴Akira Yoshiasa,⁵Tomoko Sato,⁶Takamichi Kobayashi,⁷Akihisa Mori
American Mineralogist 108, 686-694 Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P0686.pdf]
¹Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China
²Graduate School of Engineering, Osaka University, Suita 565-0871, Japan
³Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China
⁴Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
⁵Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
⁶National Institute for Materials Science, Tsukuba 305-0044, Japan
⁷Department of Mechanical Engineering, Sojo University, Kumamoto 860-0082, Japan
Copyright: The Mineralogical Society of America

Heavy meteorite impacts on Earth’s surface produce melt and vapor that are quenched rapidly and
scattered over wide areas as natural glasses with various shapes and characteristic chemistry, which
are known as tektites and impact glasses. Their detailed formation conditions have long been debated
using mineralogical and geochemical data and numerical simulations of impact melt formations. These
impact processes are also related to the formation and evolution of planets. To unravel the formation
conditions of impact-induced glasses, we performed shock recovery experiments on a tektite. Recovered samples were characterized by X-ray diffraction, Raman spectroscopy, and X-ray absorption fine
structure spectroscopy on the Ti K-edge. Results indicate that the densification by shock compression
is subjected to post-shock annealing that alters the density and silicate-framework structures but that
the local structures around octahedrally coordinated Ti ions remain in the quenched glass. The relationship between the average Ti-O distance and Ti K pre-edge centroid energy is found to distinguish the
valance state of Ti ions between Ti4+ and Ti3+ in the glass. This relationship is useful in understanding
the formation conditions of impact-derived natural glasses. The presence of Ti3+ in tektites constrains
the formation conditions at extremely high temperatures or reduced environments. However, impact
glasses collected near the impact sites do not display such conditions, but instead relatively mild and
oxidizing formation conditions. These different formation conditions are consistent with the previous
numerical results on the crater size dependence.

¹George L. Carson,¹Lindsay J. McHenry,²Brian M. Hynek,¹Barry I. Cameron, ¹Chase T. Glenister
American Mineralogist 108, 637-652 Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P0637.pdf]
¹Department of Geosciences, University of Wisconsin-Milwaukee, 3209 N. Maryland Avenue, Milwaukee, Wisconsin 53211, U.S.A.
²Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 1234 Innovation Drive, Boulder, Colorado 80303, U.S.A.
Copyright: The Mineralogical Society of America

Iceland’s Námafjall geothermal area exhibits a range of alteration environments. Geochemical and
mineralogical analyses of fumaroles and hot springs interacting with Holocene basaltic lavas at Hverir,
and with Pleistocene hyaloclastites atop nearby Námaskarð hill, reveal different patterns of alteration
depending on water-rock ratio, degree of oxidation, and substrate composition and age. The focus of
this study is on the mineral deposits at and near hot springs at Hverir and Námaskarð. Surface samples,
and samples collected from shallow pits in the alteration aprons adjacent to hot springs, were analyzed
by X-ray diffraction (XRD) and X-ray fluorescence (XRF) to constrain the differences in composition
with both distance and depth. Fluids were analyzed in the field for their environmental parameters and
sampled for cation and anion analysis. Fluid analyses revealed uniformly acidic conditions but with
site-to-site variation in other parameters such as temperature, salinity, and conductivity. Solid phases
identified include amorphous silica, pyrite, elemental sulfur, and kaolinite in the muds, surrounded by
Fe2+-sulfate and then Fe3+-sulfate efflorescence, following a redox gradient pattern involving the oxidation of sulfur and then iron with increasing distance. Shallow pits excavated near two Námaskarð hot
springs reveal a shallow oxidation front, with sulfide-rich materials below a thin surface of sulfates and
elemental sulfur. Silica phases include amorphous silica and quartz. Quartz likely reflects diagenetic
maturation of earlier-formed amorphous silica, under surface hydrothermal conditions.
The high iron content of the substrate basalt and the prevalence of Fe-sulfates and Fe-oxides among
the alteration products make this geothermal area an especially useful analog for potential martian
hydrothermal environments. In particular, these sulfate-rich deposits adjacent to volcanic, acidic hot
springs could provide a helpful comparison for sulfur-rich soils in the Columbia Hills on Mars, where
some of the same minerals have been identified (e.g., ferricopiapite) or inferred (e.g., rhomboclase).