F♭ Phrygian — 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 · i7Fbm7
Degree 2 · IImaj7Gbbmaj7
Degree 3 · III7Abb7
Degree 4 · iv7Bbbm7
Degree 5 · v°7Cbm7b5
Degree 6 · VImaj7Dbbmaj7
Degree 7 · vii7Ebbm7