Skip to main content

Thermodynamic properties and crystal structure refinement of ferricopiapite, coquimbite, rhomboclase, and Fe2(SO4)3(H2O)5

Buy Article:

$30.00 plus tax (Refund Policy)


Enthalpies of formation of ferricopiapite [nominally Fe4.67(SO4)6(OH)2(H2O)20], coquimbite [Fe2(SO4)3(H2O)9], rhomboclase [(H3O)Fe(SO4)2(H2O)3], and Fe2(SO4)3(H2O)5 were measured by acid (5 N HCl) solution calorimetry. The samples were characterized by wet chemical analyses and synchrotron powder X-ray diffraction (XRD). The refinement of XRD patterns gave lattice parameters, atomic positions, thermal factors, and occupancies of the sites. The calculated formulae differ slightly from the nominal compositions: Fe4.78(SO4)6(OH)2.34(H2O)20.71 (ferricopiapite), (Fe1.47Al0.53)(SO4)3(H2O)9.65 (coquimbite), (H3O)1.34Fe(SO4)2.17(H2O)3.06 (rhomboclase), and Fe2(SO4)3(H2O)5.03. All thermodynamic data are given per mole of these formulae.

The measured standard enthalpies (in kJ/mol) of formation from the elements (crystalline Fe, Al, S, and ideal gases O2 and H2) at T = 298.15 K are −4115.8±4.1 [Fe2(SO4)3(H2O)5.03], −12045.1±9.2 (ferricopiapite), −5738.4±3.3 (coquimbite), and −3201.1±2.6 (rhomboclase). Standard entropy (Sº) was estimated as a sum of entropies of oxide, hydroxide, and sulfate components. The estimated Sº (in J/mol·K) values for the iron sulfates are 488.2 [Fe2(SO4)3(H2O)5.03], 1449.2 (ferricopiapite), 638.3 (coquimbite), and 380.1 (rhomboclase). The calculated Gibbs free energies of formation (in kJ/mol) are −3499.7±4.2 [Fe2(SO4)3(H2O)5.03], −10089.8±9.3 (ferricopiapite), −4845.6±3.3 (coquimbite), and −2688.0±2.7 (rhomboclase). These results combined with other available thermodynamic data allow construction of mineral stability diagrams in the FeIII 2(SO4)3–FeIISO4–H2O system. One such diagram is provided, indicating that the order of stability of ferric sulfate minerals with decreasing pH in the range of 1.5 to −0.5 is: hydronium jarosite, ferricopiapite, and rhomboclase.


Document Type: Research Article


Publication date: March 1, 2006

More about this publication?
  • The European Journal of Mineralogy publishes original papers, review articles and letters dealing with the mineralogical sciences s.l. These include primarily mineralogy, petrology, geochemistry, crystallography and ore deposits, as well as environmental, applied and technical mineralogy. Nevertheless, papers in any related field, including cultural heritage, will be considered.
  • Editorial Board
  • Information for Authors
  • Submit a Paper
  • Subscribe to this Title
  • Terms & Conditions
  • Ingenta Connect is not responsible for the content or availability of external websites

Access Key

Free Content
Free content
New Content
New content
Open Access Content
Open access content
Partial Open Access Content
Partial Open access content
Subscribed Content
Subscribed content
Free Trial Content
Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more