allagite
/ˈaləɡʌɪt/Mineralogy. Now rare
noun
A green or brownish-red mineral of uncertain identity (perhaps an altered form of rhodonite) consisting of a silicate and carbonate of manganese.
Origin
Early 19th century. From German Allagit from ancient Greek ἀλλαγή change, alteration (from ἄλλος other; the guttural suffix is unexplained) + German -it, with alteration of the ending after words in -ite; the mineral was apparently so called on account of its change of appearance on exposure.