Kristalografsko-mineraloške karakteristike alunita i natroalunita sa Velikog Bukovika kod Raške

Abstract

Alunite and natroalunite from Veliki Bukovik near Raška were determined with the X-ray diffraction analysis. There were obtained following unit cell dimensions and crystallochemical formulas: alunite: a0=6,976(1)Å, c0=17,295(6)Å, V0=729,0(3)Å3, c0/a0=2,479 (K0,83(H3O)+0,17)1,00Al3,00(S0,99O4)2(OH)6. natroalunite: a0=6,981(1)Å, c0=16,884(6)Å, V0=712,6(3)Å3, c0/a0=2,419 (Na0,50K0,38(H3O)+0,12)1,00(Al2,95Fe0,13)3,08(S0,99O4)2(OH)6. jarosite: a0=7,291(4)Å, c0=17,23(2)Å, V0=793(1)Å3, c0/a0=2,363. At alunite and natroalunite considerable part of the alkalies was exchanged with the hydronium ion, which indicates to the transition to hydroalunite and hydronatroalunite. Presence of the hydronium ion in the structures of these minerals also indicates to the low temperature and low pressure of the formation, at acid conditions and with high sulphate activity.