19-tone

The chromatic scale is created by dividing an octave into 12 equal parts. But there is no reason why the octave can't be divided in other ways.

Some musicians have experimented with dividing the octave into 19 notes, and have written music using this 19-tone scale.

The notes labeled 1 are identical to Cs in the conventional chromatic scale and are exactly an octave apart. All of the other notes are between the cracks of the notes in the chromatic scale.

And more...

Scales are a kind of musical abstraction. They're an ordered collection of notes that can serve as a palette of notes for a musician to choose from. The scale examples in these lessons represent just a small sampling of the huge number of possible scales.