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The Mines and Minerals of Lavrion - Ammoniojarosite

Last Updated: 21st Mar 2020

By Branko Rieck

AMMONIOJAROSITE, (NH4)Fe3+3(SO4)2(OH)6, trigonal

General Appearance
The authors of the original publication of katerinopoulosite (Chukanov et al. 2018) describe among its paragenesis also ammoniojarosite. From samples taken in spring 2017 by the author this could be confirmed. For analysis ICP-OES was used, from which the following formula was calculated: [(NH4)0.75Na0.14K0.10Mg0.01]Fe3.01(SO4)2(OH)6 which corresponds to a slightly Na- and K-bearing ammoniojarosite and is in good agreement with analytical results reported by Palache et al. (1951). Other samples found only traces of Na, Cu and As (SEM-EDS) (Kolitsch, 2019, pers. comm.). Ammoniojarosite forms yellow to light brown aggregates, often precipiated as multiple generations overgrowing each other (see Figure 3).

Ammoniojarosite: pseudocubic with {01.2} and small {0001}
Ammoniojarosite: platy with {01.2} and large {0001}
Ammoniojarosite: pseudocubic with {01.2} and small {0001}
Ammoniojarosite: platy with {01.2} and large {0001}
Ammoniojarosite: pseudocubic with {01.2} and small {0001}
Ammoniojarosite: platy with {01.2} and large {0001}

Ammoniojarosite is directly accompanied by gypsum, atacamite, katerinopoulosite, nickelboussingaultite, aurichalcite, ktenasite and a further as yet undefined ammonium-bearing phase. In the wider area also goslarite, melanterite, chalcanthite, natrochalcite, Zn-bearing humboldtine and epsomite are found.

It must be pointed out that ammoniojarosite is an exceedingly rare mineral in this paragenesis. Only in a small cavity dubbed "rathole" by collectors (because of an abandoned nest of a dormouse found inside) analytically confirmed discoveries of this mineral could be made (the vast majority of jarosite in this area is either plain jarosite or, to a small percentage, natrojarosite).

Fig. 1: Green, pseudo-octahedral composite atacamite crystals (SXRD- and SEM-EDS-analysed) on yellow-brownish crusts of a Na-bearing ammoniojarosite (SEM-EDS-analysed). The colourless, glassy phase is not analysed, but is probably only etched gypsum. FOV: 3.5 mm.

Fig. 2: SEM micrograph (BSE mode) of pseudocubic ammoniojarosite crystals. As foreign elements, only traces of Na, Cu and As were detectable by SEM-EDS analyses.

Fig. 3: SEM micrograph (BSE mode) of a second generation of ammoniojarosite forming pale yellow finely crystalline aggregates of tiny pseudocubic crystals which grew on a first generation brown-yellow, coarser ammoniojarosite.

Thanks go to Dr. Uwe Kolitsch for constructive comments and diligent proofreading to improve this article.

Chukanov, N.V., Pekov, I.V., Belakovskiy, D.I., Britvin, S.N., Stergiou, V., Voudouris, P., Magganas, A. (2018) Katerinopoulosite, (NH4)2Zn(SO4)2·6H2O, a new mineral from the Esperanza mine, Lavrion, Greece. European Journal of Mineralogy: 30: 821-826.
Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy, (7th edition), v. II, 562–563.
Rieck, B., Kolitsch, U., Voudouris, P., Giester, G. and Tzeferis, P. (2018): Weitere Neufunde aus Lavrion, Griechenland. Mineralien-Welt 29 (5), 32-77 (in German).

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