A rare reddish-brown or pink mineral consisting of a basic arsenate of manganese, typically occurring as prisms and as crusts on manganese ores.
Chemical formula: Mn₇(AsO₄)₂(OH)₈. Crystal system: monoclinic.
Late 19th century; earliest use found in Journal of the Chemical Society. From Swedish allaktit from ancient Greek ἀλλακτ-, stem of ἀλλάσσειν to change (ultimately from ἄλλος other; the guttural suffix is unexplained) + Swedish -it. So called because of the property of changing colour in polarized light depending on the orientation of the crystals (pleochroism).