|natural minor scale||R||2||♭3||4||5||♭6||♭7|
The Locrian mode is a medieval mode starting on the seventh degree of the diatonic scale, with half steps between the first and second degrees and fourth and fifth degrees. Of all the modes, it is the most alien upon the ear and the least usable. Think of it as an altered Phrygian. To be precise, it is a minor scale with a flat 7th, flat 5th, and flat 2nd (or 9th), so we can call it a minor7♭5♭9. A chord with this many alterations is densely altered and therefore restricted in its usefulness. But this doesn't rule the Locrian out altogether. Its dark, sinister feel was put to good use by Metallica in "Enter the Sandman" and "Sad But True", and by Black Sabbath in "Symptom of the Universe". The Locrian also crops up quite often in middle-eastern and Jewish music.