• journal_title：Mineralogical Magazine
• Contributor：I. E. Grey ; N. V. Y. Scarlett ; H. E. A. Brand
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2013-04-01
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2013.077.3.03
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：77
• issue：3
• firstpage：249
• section：Articles

id="p-1">Syntheses in acidified hydrothermal (HT) solutions (1 n H₂SO₄ or stronger) produce monoclinic non-stoichiometric K-jarosites which contain Fe-site vacancies with long-range order. Syntheses in non-acidified HT solutions produce rhombohedral K-jarosites which contain relatively large numbers of Fe-site vacancies with no long-range order. Increasing the [Fe]/[K] ratio, reaction temperature and reaction time in non-acidified solutions promotes the formation of monoclinic jarosites which contain Fe-site vacancies with short-range order. A structural model including details of the ordering of the Fe-site vacancies was obtained by refinement of single-crystal synchrotron data from one of the HT synthesis products; this model was used to refine synchrotron powder X-ray diffraction data from products synthesized at different reaction times, temperatures and [Fe]/[K] ratios. Thermal and chemical analyses are consistent with a model for non-stoichiometry in which domains of stoichiometric jarosite are intergrown with butlerite-like iron-deficient domains with a composition [Fe₂(SO₄)₂(OH)₂(H₂O)₄]. It was found that heterogeneous nucleation of monoclinic jarosite on Si disks is preceded by the formation of an oriented film of Maus's Salt, K₅Fe₃O(SO₄)₆·10H₂O, as a precursor phase, and that this transforms topotactically into oriented jarosite, which contains butlerite-like layers parallel to the disk surface. Structural models for the transformation of Maus's Salt into jarosite are proposed.