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 Ca_0.46(K+Na)_0.10 (Na>>K) to Ca_0.35(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, Ca_0.5Al₃ (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.

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We evaluated the diffusion coefficients of Fe–Mg and Ca in olivine reported in several literatures by analyzing the diffusion profiles experimentally produced. Both the Fe and Ca contents of olivine in run products drastically increase toward the rim within a few tens of micrometers probably due to atomic diffusion from the surrounding Fe- and Ca-rich melt. The chemical zoning profiles of olivine measured with an electron microprobe were compared with those calculated by numerically solving the diffusion equation by using different diffusion coefficients. The diffusion coefficient of Fe–Mg in olivine reported by Misener (1974) gives a better fit than that by Buening and Buseck (1973), that is, the latter is too large. The diffusion coefficient of CaO in olivine reported by Jurewicz and Watson (1988b) gives a better fit than that by Morioka (1981), that is, the latter is too small. Our calculations for analyzing chemical zoning on the basis of atomic diffusion successfully reproduce the curvature of a profile experimentally made by diffusional modification of initial uniform profile of olivine.

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