piano scale
D Locrian
D1E♭♭2F♭3G4A♭♭5B♭♭6C♭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
DHE♭WFWGHA♭WB♭WCWD
What is true of it
D Locrian is D, E♭, F, G, A♭, B♭ and C, and back to D.
Its steps are H – W – W – H – W – W – W, where W is a whole step and H a half.
On the same tonic, D Phrygian differs from it by exactly one note.
Chords made only of these notes
CmminorCm7minor seventhDdimdiminishedDm7♭5half-diminished seventhE♭majorE♭maj7major seventhFmminorFm7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.