If you are thinking of learning heavy metal guitar, then you should know that there are no particular set of rules involved in the process. However, there is a musical legacy and unwritten sets of notions that the metal guitarists generally follow. This general idea is applicable for heavy metal guitar scales as well. You can play metal guitar by following whichever scale you want, but the general trend is to use minor scales because the ultimate aim is to produce a heavy and guttural sound.
The pentatonic scale is probably most often used in heavy metal guitar but there are hosts of other scales, which really complement the dark and brooding mood of the music. Some of them are Phrygian, Harmonic Minor and Byzantine. The natural minor scale, that is the Aeolian scale and the Spanish Gypsy and the Locrian scales are also used in certain cases. Since much of heavy metal draws a lot of influence from blues, therefore some of the blues scales are also in use. In fact pentatonic scale itself is derived from the blues and the rock tradition.
The second most common scale in heavy metal is probably the natural minor scale. It is sometimes used along with the pentatonic scale but is capable of a greater symphony. You can find a lot of Metallica performance in Aeolian scale. However, this scale cuts across various genres and is popular with death metal players as well. The Harmonic Minor, which is a slight variation of the Aeolian scale, is also universally popular with the metal guitar players.
The Phrygian scale is a very exotic Spanish flavored scale and is also commonly used by many metal guitarists. This particular kind of guitar playing pattern has been popularized by Yngwie Malmsteen and is very evident in most of the guitar solos in his albums. By mixing in fast guitar playing techniques, you can also fuse other genres of music with metal guitar playing. One example of this is the neo-classical music that Malmsteen plays. On the other hand, the Locrian scale is only used by more brooding and offbeat metal bands mainly belonging to the death metal genre.
So, there are indeed many heavy metal guitar scales apart from the basic pentatonic scale. It is true that certain chords and riffs play better in some scales than the others. Therefore, if you learn all the scales by heart, you can modify your performance according to the situation.
