Diminished 7th chord (dim7): formula 1 ♭3 ♭5 ♭♭7. Minor 3rds stacked all the way: symmetrical and very tense, it works as a passing chord and as a dominant with a ♭9.
Diminished 7th chord (dim7): formula 1 ♭3 ♭5 ♭♭7. Minor 3rds stacked all the way: symmetrical and very tense, it works as a passing chord and as a dominant with a ♭9.