Arsenoclasite
arsenate mineral

Arsenoclasite (originally arsenoklasite) is a red or dark orange brown mineral with formula Mn5(AsO4)2(OH)4. The name comes from the Greek words αρσενικόν (for arsenic) and κλάσις (for cleavage), as arsenoclasite contains arsenic and has perfect cleavage. The mineral was discovered in 1931 in Långban, Sweden.
Description
Arsenoclasite is red or dark orange brown in color. The mineral rarely occurs as crystals; rather it has either a massive or granular habit. When crystals are present, they are no larger than 5 millimetres (0.20 in). Arsenoclasite has been found in association with adelite, allactite, barite, calcite, dolomite, gatehouseite, hausmannite, hematite, manganoan ferroan calcite, sarkinite, and shigaite. The mineral occurs in fissures of metamorphosed Fe-Mn ore bodies and sedimentary Fe-Mn deposits.
Structure
A 1971 study identified the mineral's structure as an array of oxygen atoms in a double hexagonal close packed pattern. However, a 1977 study discovered that all the manganese ions in arsenoclasite are six-coordinated, a constraint this structure cannot permit without severe distortion.
“Arsenoclasite” enters the record as arsenate mineral. Crown Archives preserves that source wording while asking what Arsenoclasite, arsenate and mineral can confirm, complicate or overturn.
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