C♯ Mixolydian — 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 · I7C#7
Degree 2 · ii7D#m7
Degree 3 · iii°7E#m7b5
Degree 4 · IVmaj7F#maj7
Degree 5 · v7G#m7
Degree 6 · vi7A#m7
Degree 7 · VIImaj7Bmaj7