Abstract
<p> An exceptional new occurrence of the mineral tamarugite, NaAl(SO <sub> 4 </sub> ) <sub> 2 </sub> · 6H <sub> 2 </sub> O, from a short karst cavity (Diana Cave, Băile Herculane; SW Romania) is described. It was formed by corrosion of the bedrock (limestone and marls) by a SO <sub> 4 </sub> <sup> 2− </sup> -rich steam condensate resulting from oxidized S <sup> 2− </sup> ions escaping from the thermo-mineral water emerging from depth in the cave. Tamarugite forms dull white earthy aggregates. Scanning-electron microscope (SEM) observations reveal tabular subhedral crystals never exceeding 15 μm across. The cell parameters refined from the powder data for the monoclinic space group <em> P </em> 2 <sub> 1 </sub> / <em> a </em> are: <em> a </em> = 7.358(6), <em> b </em> = 25.23(2), <em> c </em> = 6.093(5) Å, <em> β </em> = 95.16(5) °, <em> V </em> = 1126.98(1) Å <sup> 3 </sup> . The δ <sup> 34 </sup> S values of the cave sulphates and the thermal water confirm marine evaporites as the source of sulphur. The sulphate-acid alteration of limestone with contribution of Al <sup> 3+ </sup> and Na <sup> + </sup> from the marls and the thermal water is responsible for the formation of tamarugite. The steam-condensate alteration paragenesis includes native sulphur, bassanite, anhydrite, epsomite, pickeringite, halotrichite, apjohnite and alunite, as well as quartz and halite, all primary and secondary speleogenetic by-products.</p>
Original language | American English |
---|---|
Journal | European Journal of Mineralogy |
Volume | 25 |
DOIs | |
State | Published - Sep 1 2013 |
Keywords
- tamarugite
- thermo-mineral waters
- team-condensate alteration
- cave minerals
- sulphuric acid speleogenesis
- sulphates
- Cerna Valley
- Romania