 Experimental procedures in this report summarize attempts to synthesize potassium-,
hydronium-, sodium-, and mixed-composition (hydronium-bearing) jarosites.
After experimentation, some acceptable combinations of chemical and physical
factors were found to routinely synthesize chemically different jarosites,
which were used as part of a characterization study of some natural and
synthetic jarosites.
Jarosite is a sulfate mineral that is common in
geologic settings where iron sulfide minerals such as pyrite or marcasite
are subject to oxidative weathering.
The presence of jarosite is a hallmark of acidic conditions. Jarosite forms
as a secondary mineral in weathered sulfidic ores, coal mine wastes,
on oxidizing mine wastes, and in streams affected by acid mine
drainage. Jarosite also forms in acid-sulfate soils, as an alteration
product of sulfidic shales, and in hydrothermal environments.
Because
of its important role in earth surface processes, the USGS is conducting
mineralogical, geochemical, and remote sensing studies to characterize natural jarosites and to elucidate its
stability range and conditions of formation.
The presence of jarosite
is not limited to the Earth. The recent identification of jarosite in
the rocks at the Meridiani Planum on Mars has given planetary geologists
reason to think that jarosite may be evidence of relict lacustrine (lake
systems) or hydrothermal (water enriched magma emanations) systems on
the Martian surface. USGS scientists are currently developing jarosite
detection systems that can be placed on orbiting spectrometers. One day
these systems may guide Mars landers to sites abundant in jarosite, sites
most likely to have sheltered ancient Martian life.
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