piano scale
F Locrian
F1G♭♭2A♭♭3B♭4C♭♭5D♭♭6E♭♭7
The only mode of the major scale whose fifth is diminished, which is why its tonic chord cannot rest.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
FHG♭WA♭WB♭HC♭WD♭WE♭WF
What is true of it
F Locrian is F, G♭, A♭, B♭, C♭, D♭ and E♭, and back to F.
Its steps are H – W – W – H – W – W – W, where W is a whole step and H a half.
It costs 6 alterations to write — near the limit of what a key signature can carry.
On the same tonic, F Phrygian differs from it by exactly one note.
Chords made only of these notes
D♭majorD♭7dominant seventhE♭mminorE♭m7minor seventhFdimdiminishedFm7♭5half-diminished seventhG♭majorG♭maj7major seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.