Abstract
Huangite was found from the type locality of minamiite in sulphuric altered andesite from Okumanza, Gunma Prefecture, Japan. EDS analyses indicate that “alunite” crystals are composed of very minute intergrowth of alunite, natroalunite, minamiite and huangite. The domain corresponding to each species are 5 to 100 μm in width. In the present huangite the ranges of A-site cations in general formula of alunite group minerals, AB3(SO4)2(OH)6, vary from Ca0.46(K+Na)0.10 (Na>>K) to Ca0.35(K+Na)0.26 (K>Na) on the basis of Al = 3, that is, they correspond to approximately 90∼70 % mole of huangite end member, Ca0.5Al3 (SO4)2 (OH)6. Distinct compositional gaps are observed between 55 to 80 % Ca mole on Na - Ca join and 5 to 60 % Ca mole on K - Ca join in K - Na - Ca diagram of alunite group mineral.
