ˌsinəˈdelˌfīt noun
( -s )
Etymology: German synadelphit, from Greek synadelphos one that has a brother or sister (from syn- + adelphos brother) + German -it -ite — more at -adelphous
: a mineral (Mn,Mg,Ca,Pb)(AsO 4 )(OH) 5 composed of a basic arsenate of manganese often with other elements (as magnesium, calcium, lead) and occurring in black prismatic crystals and grains (hardness 4.5, specific gravity 3.5)