allactite
/əˈlaktʌɪt/Mineralogy
noun
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..
Origin
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).