A previously unknown piece of music written by Wolfgang Amadeus Mozart has been discovered in Leipzig, the city said on Thursday. The 12-minute piece, “Serenate ex C,” is from the collection of Carl Ferdinand Becker and was part of the music collection of the Leipzig City Libraries, according to the city. Researchers suggest Mozart (1756-1791) wrote the piece during the mid to late 1760s, when he was a teenager. The composition was presented at the International Mozarteum Foundation in Salzburg. It is to be performed at the Leipzig Opera on Saturday, September 21. Researchers unearthed the mus…