¹Christopher T. Adcock,¹Elisabeth M. Hausrath,²Elizabeth B. Rampe,³Hexiong Yang,³Robert T. Downs
American Mineralogist 108, 430-438Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P0430.pdf]
¹Department of Geoscience, University of Nevada, Las Vegas, 4505 S. Maryland Parkway, Las Vegas, Nevada 89154-4010, U.S.A.
²NASA Johnson Space Center, 2101 E NASA Parkway, Houston, Texas 77058, U.S.A. 3
Department of Geosciences, University of Arizona, 1040 East 4th Street, Tucson, Arizona 85721-0077, U.S.A.
Copyright: The Mineralogical Society of America

Investigations of planetary processes using phosphate minerals often focus on igneous, recrystallized, or potentially metasomatized minerals, likely as a result of the minerals commonly available for
study within meteorites and lunar samples. However, Mars is a relatively phosphorus-rich planet and
possesses abundant evidence of past aqueous surface interactions. Therefore, secondary phosphate
phases may be important on the martian surface. Giniite [Fe2+Fe4
3+(PO4)4(OH)2·2H2O] is a secondary
phosphate mineral that has been suggested as a potentially significant phase at locations in Gusev Crater
and Meridiani Planum on Mars. Although relatively rare as a natural mineral on Earth, giniite has gained
attention as an important mineral in industry and technology, especially the lithium battery industry,
and the ferrian version of the mineral is often synthesized. This suggests giniite may be important as
an in situ resource utilization (ISRU) target for future extended human missions to Mars. Despite this,
there are few data available on the natural mineral and the last characterization of the structure was
over 40 years ago. There has also been confusion in the literature as to whether giniite is orthorhombic
or monoclinic. In this work we revisit and document the chemistry and crystal structure of natural
giniite from the type locality at the Sandamab pegmatite in Namibia using updated techniques. Our
results refine and update what was previously known regarding the structure and chemistry of giniite
and support the potential of the mineral as a possible martian scientific and resource target for further
study to aid future missions

¹George L. Carson,¹Lindsay J. McHenry,²Brian M. Hynek,¹Barry I. Cameron, ¹Chase T. Glenister
American Mineralogist 108, 409-429 Link to Article [http://www.minsocam.org/msa/ammin/toc/2023/Abstracts/AM108P0409.pdf]
¹Wisconsin-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 Námaskar∂, reveal different patterns of alteration
depending on the water/rock ratio, degree of oxidation, and substrate composition and age. The focus
of this study is a transect of a Hverir fumarole that has formed a bullseye pattern of alteration of a
Holocene basaltic lava flow. Surface samples and samples collected from shallow pits were analyzed
by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM) to
constrain changes in mineral assemblage and major elemental composition with both distance and
depth. Elemental sulfur is concentrated near the vent, with leached deposits with amorphous silica
and anatase nearby and kaolinite, hematite, and jarosite/alunite-group sulfate minerals farther out,
with smectites and less altered material at the margins, though smaller-scale mineralogical diversity
complicates this pattern.
Silica phases include amorphous silica (most samples), cristobalite (some samples in the leached
part of the apron), and quartz (minor constituent of a few samples). The silica was concentrated through
residual enrichment caused by leaching and is accompanied by a significant enrichment in TiO2 (in
anatase). The presence of abundant cristobalite in a surface fumarole-altered Holocene basaltic lava
flow most likely reflects cristobalite formed during the devitrification of volcanic glass or precipitation
from fumarolic vapors, rather than high-temperature processes. Minor, localized quartz likely reflects
diagenetic maturation of earlier-formed amorphous silica, under surface hydrothermal conditions.
Natroalunite, natrojarosite, and jarosite are all present and even exhibit compositional zonation within
individual crystals, showing that under surface hydrothermal conditions, these minerals can form a
significant solid solution.
The high iron content of the substrate basalt and the prevalence of Fe-sulfates and Fe-oxide spherules
among the alteration products makes this geothermal area an especially useful analog for potential
martian hydrothermal environments. The residual enrichment of silica in the leached deposits of the
Hverir fumarole apron could serve as an acid-sulfate leaching model in which amorphous silica forms
without appreciable sulfur-bearing phases in many samples, a possible analog for silica-rich soils in
the Columbia Hills on Mars. The coexistence of hematite spherules and jarosite-group minerals serves
as an intriguing analog for a volcanic/hydrothermal model for hematite and jarosite occurrences at
Meridiani Planum.