Étude Op. 25, No. 6 (Chopin)
Étude Op. 25, No. 6, in G-sharp minor, is a technical study composed by Frédéric Chopin focusing on thirds, trilling them at a high speed. Also called the Double Thirds Etude, Op. 25, No.6 is considered one of the hardest of Chopin's 24 Etudes, ranking the highest level of difficulty according to the Henle difficulty rankings.
Excerpt from the beginning of the Étude Op. 25 No. 6