The Locrian mode corresponds to the white keys from B to B. Its unique feature is a diminished fifth above the tonic instead of a perfect one. Because of this the tonic triad comes out diminished and unstable, and the mode seems to lose the ground beneath its feet: there is no reliable anchor to which one wishes to return.
It is precisely this instability that kept the Locrian mode almost unused in classical music as an independent foundation. In the 20th–21st centuries, however, it became a valuable expressive means: jazz musicians use it over half-diminished chords, and metal bands for a sense of anxiety and chaos. The Locrian mode is theoretically the outermost edge of the diatonic scale — a scale that forever “hangs” in tension, never finding rest.
