piano scale
A Locrian
A1B♭♭2C♭3D4E♭♭5F♭6G♭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
AHB♭WCWDHE♭WFWGWA
What is true of it
A Locrian is A, B♭, C, D, E♭, F and G, and back to A.
Its steps are H – W – W – H – W – W – W, where W is a whole step and H a half.
On the same tonic, A Phrygian differs from it by exactly one note.
Chords made only of these notes
Found by testing every chord in the catalogue against these 7 sounds, not chosen.