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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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ISSN
1945-3027
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Volume 100, Issue 1

Issues

Hydrothermal Synthesis And Crystal Structure Of Also4(Oh): A Titanite-Group Member

Alan J. Anderson
  • Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Hexiong Yang / Robert T. Downs
Published Online: 2015-01-10 | DOI: https://doi.org/10.2138/am-2015-5160

Abstract

Aluminum hydroxysulfate, AlSO4(OH), is postulated to play a vital role in controlling the solubility of aluminum in sulfate-rich acidic soils and ground waters, but it has not yet been confirmed in nature. This study reports the synthesis of an AlSO4(OH) crystal at 700 °C and ~1.0 GPa in a hydrothermal diamond-anvil cell from a mixture of 95% H2SO4 and Al2O3 powder and its structure determination from single-crystal X‑ray diffraction data. AlSO4(OH) is monoclinic with space group C2/c and unitcell parameters a = 7.1110(4), b = 7.0311(5), c = 7.0088(4) Å, b = 119.281(2)°, and V = 305.65(3) Å3. Its crystal structure is characterized by kinked chains of corner-sharing AlO6 octahedra that run parallel to the c-axis. These chains are linked together by SO4 tetrahedra and hydrogen bonds, forming an octahedral-tetrahedral framework. Except for the numbers and positions of H atoms, AlSO4(OH) is isostructural with the kieserite-type minerals, a subgroup of the titanite group of minerals. A comparison of powder X‑ray diffraction patterns indicates that our AlSO4(OH) is the same as that obtained by Shanks et al. (1981) through hydrolysis of Al2(SO4)3 solutions at temperatures above 310 °C. To date, AlSO4(OH) has been synthesized only at temperatures above 290 °C, implying that it may not stable in low-temperature environments, such as acidic soils and mine waters. The possible environments to find Al(OH)SO4 may include places where sulfur-rich magma-derived fluids react with aluminous rocks under elevated temperature and pressure, and on Venus where a sulfur-rich atmosphere interacts with surface rocks at temperatures above 400 °C.

Keywords : AlSO4(OH); aluminum hydroxysulfate; X‑ray diffraction; crystal structure; Raman spectroscopy; high temperature

About the article

Received: 2014-08-12

Accepted: 2014-09-26

Published Online: 2015-01-10

Published in Print: 2015-01-01


Citation Information: American Mineralogist, Volume 100, Issue 1, Pages 330–333, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-5160.

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© 2015 by Walter de Gruyter Berlin/Boston.

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