G-flat major Rondo-Finale of his Seventh Symphony. Mahler's Tenth Symphony was composed in the enharmonic key of F-sharp major. This key is more often found in piano music, as the use of all five black keys allows an easier conformity to the player's hands, despite the numerous flats. Austrian composer Franz Schubert chose this key for his third impromptu from his first collection of impromptus (1827). Polish composer Frédéric Chopin wrote two études in the key of G-flat major: Étude Op. 10, No. 5 "Black Key" and Étude Op. 25, No. 9 "Butterfly". French composer Claude Debussy used this key for one
D-flat major while for the return of the second theme in the first movement. Claude Debussy also switches from D-flat major to C-sharp minor in the significant section in his famous "Clair de lune". Antonín Dvořák's "New World Symphony" likewise switches to C-sharp minor for a while for the significant section in the slow movement. D-flat major is enharmonic to C-sharp major. In music for the harp, D-flat major would be preferable, not only because harp strings are more resonant in the flat position and the key has fewer accidentals, but also because modulation to the dominant key is easier (by putting