The String Quartet No. 6 in F minor, Op. 80 was composed by Felix Mendelssohn in 1847. It was the last major piece he completed before he died two months later on 4 November 1847. He composed the piece as an homage to his sister Fanny who had died on 17 May of that year and it bore the title "Requiem for Fanny." (Wikipedia)
Sheet music and audio is from IMSLP under Creative Commons License.
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Performers: Musopen String Quartet (musopen.org/)