A♭ Locrian — 7th chords
Four-note stacks of thirds on each degree — root, 3rd, 5th, 7th. The added 7th gives jazz, gospel, and modern classical voicings their distinctive colour.
All 7 seventh chords in sequence
Degree 1 · i°7Abm7b5
Degree 2 · IImaj7Bbbmaj7
Degree 3 · iii7Cbm7
Degree 4 · iv7Dbm7
Degree 5 · Vmaj7Ebbmaj7
Degree 6 · VI7Fb7
Degree 7 · vii7Gbm7