Ammonium minerals from burning coal-dumps of the Upper Sileian Coal Basin (Poland)

Assemblages composed of 11 ammonium min er als, mainly sulphates and chlorides, were recorded from four burning coal-dumps (BCD) in the Upper Silesian Coal Ba sin. Most of them are newly recorded from Poland. Minerals were identified using PXRD and SEM with EDS analyses. Salammoniac, NH4Cl, and tschermigite, (NH4)Al(SO4)2ź12H2O are the most common species on the BCD studied. Kremersite, (NH4,K)2[FeCl5(H2O)], is rare and coexists with members of the ammonioalunite–ammoniojarosite series. Boussingaultite, (NH4)2Mg(SO4)2ź6H2O, and more rarely clairite, (NH4)2Fe3(SO4)4(OH)3ź3H2O, and mascagnite, (NH4)2SO4, ac company numerous Mg, Al, Fe and Ca sulphate minerals. These usually occuras very fine admixtures forming coatings, small nodules or porous masses and were found on the BCD surface close to gas vents. Also a massive sulphate crust was found in the deeper part of the BCD nearby the fire zone. This crust is composed mainly of an hydrous sulphates: godovikovite, (NH4)(Al,Fe)(SO4)2 , and very minor sabieite, (NH4)Fe(SO4)2, and efremovite, (NH4)2Mg2(SO4)3, which were transformed into different hydrated sulphates in the outer zone of the crust. The fibrous or dendritic habit of many ammonium minerals, and the vesicular texture of some sulphate aggregates, point to their crystallization from the gas phase. Some ammonia miner ls may also have developed through hydration of prevlously formed phases or precipitated from locally formed aqueous solutions due to cooling or evaporation. The appear ance of ammonia minerals on BCD can be a useful indicator of the presence of underground fires.