An Etymological Dictionary of the German Language/Annotated/Karfunkel
Karfunkel, masculine, ‘carbuncle,’ from Middle High German karbunkel, masculine, with the variant karfunkel, probably based on Middle High German vunke, Modern High German Funke; b is the original sound, for the word is based upon Latin carbunculus (compare English carbuncle, Modern French escarboucle).