piano scale
G Phrygian
G1A♭♭2B♭♭3C4D5E♭♭6F♭7
Minor with a flattened second — the half step right above the tonic is the whole character.
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
GHA♭WB♭WCWDHE♭WFWG
What is true of it
G Phrygian is G, A♭, B♭, C, D, E♭ and F, and back to G.
Its steps are H – W – W – W – H – W – W, where W is a whole step and H a half.
On the same tonic, G natural minor 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.