PROCESS OF FORMATION OF As-BEARING MINERALS AND ARSENATES UNDER SURFACE OF THE EARTH

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The new mineral, pararsenolamprite, the third polymorph of native As, was found from the Mukuno mine, Oita Prefecture. Pararealgar, alacranite, dufrenoysite, claudetite, wallkilldellite and arseniopleite are found as the first occurrence in Japan. The primary As-bearing minerals are mostly S-bearing compounds, and As is oxidized to penta-valent state when their minerals were altered. The tri-valent As (arsenic oxide, so called arsenious acid) is only found as the altered material from native As. Around mining areas As is common component of rocks and soils. However, this poisonous problem do not cause seriously, since As is included in relatively stable and insoluble arsenate minerals, that is, as penta-valent state As (arsenate). Most common arsenate mineral found under surface circumstance is scorodite. It is ferric hydrate arsenate. Schwertmannite is low crystalline hydrous ferric sulfate mineral and can include As. I forms easily in stream and then As in stream is removed. When schwertmannite becomes stable state, It may be changed to FeOOH (mostly goethite) + jaroshite + scorodite.