The Harmonic Minor Scale was developed due to the lack of dominant resolution from the V7 to I in the harmonized Natural Minor scale. In essence, it is an alteration of the Natural Minor scale "for harmonic purposes." Unlike the Natural Minor, the diatonic V of the Harmonic Minor scale is a dominant chord. In other words, you'll find a tritone relationship between the chord's 3rd and 7th degrees.
Harmonic Minor Mode Construction Diagram:
*Weird Warning: I have used the enharmonic Fb here instead of E to avoid having both Eb and E spelled out in the same scale.
You'll find unusual things going on in the Harmonic Minor scale:
1. The inclusion of both a minor 3rd and a major 7th.
2. A minor third interval between the scales 6th and 7th degrees. (this minor 3rd interval was felt to be a melodic obstacle and led to the formation of the 'Melodic Minor' scale as a further alteration of the minor scale for 'melodic purposes.' The Harmonic Minor scale was (and is) a staple element for neo-classical rock guitar. In other words, 80s shred would be quite different without this thing. Elsewhere we'll examine some applications for this scale and some of its modes.