Mineral Physics Institute Summer Scholars Program

 

Laura Podratz University of Idaho Major: Geology Mentors: Scott McLennan and Nick Tosca

Summer Project Description:

Synthesis and Stability of the Alunite-Jarosite Series

Jarosite is commonly found in several surface environments on earth, and was recently found at Meridiani Planum,
Mars by the Mössbauer spectrometer on the Mars exploration rover. Minerals in the alunite-jarosite series have the
formula AB 3 (SO 4 ) 2 (OH) 2 , where A can be potassium, sodium or hydronium, and B can be ferric iron or aluminum.

By synthesizing different compositions in the alunite-jarosite series, the spectroscopic behavior of these minerals can be
investigated systematically. Comparisons can then be made to remote spectroscopic data collected on Mars.

The first part of my project involves the synthesis of several minerals in the alunite-jarosite solid solution series.
First, I will try to synthesize minerals with potassium as the cation for the first site, and vary the ratio of aluminum
and ferric iron in the second site systematically. If successful, I will go on to synthesize minerals both with varying aluminum
and ferric iron ratios in the second site and varying the cation in the first site. By creating a complete solid solution of the
alunite-jarosite series, I will have created a database that others can use as a reference in future work, and the spectroscopic
characteristics can be tested to see if they vary as a function of composition.

The second part of my project involves testing the stability of the various jarosite minerals under different conditions.
Aqueous conditions that give rise to intermediate alunite-jarosite compositions will be investigated experimentally in the
context of surface processes on Mars. This aspect of the project has implications in planetary science, especially for the
evaporite sediments found in Meridiani Planum on Mars.

Hopefully, the two parts of the project together will help to further the understanding of the conditions in which jarosite minerals
will precipitate, and how common the various compositions are in Meridiani Planum and elsewhere.