Nowhere is Iommi’s talent for this better displayed than in his awesome (and heavy as hell) guitar work in Sabbath’s eloquent anti-war screed “War Pigs.” In the intro, he leans on the major 3 of the E chord, G#. When the up-tempo power chords kick in, he trills between the same note and the minor 3, G, further blurring the distinction between major and minor.
It’s in the song’s solo that Iommi really works his major/minor magic. The phrase below combines several Iommisms and will kill on “War Pigs” as well as on most any other heavy tune in the key of E. It starts with a slinky E Mixolydian figure. (Note that some of the Ds are open and some are fretted, which adds clang and keeps the lick from sounding too pretty.) The first ending features an Iommi-approved speed-of-light trill between E and D, while the second ending trills G (notated enharmonically as F##) to G#.
After lulling listeners into this false sense of major-key security, do what Tony would do and blaze away in the twelfth-position E minor pentatonic box. Arranging a solo with this light/dark contrast makes it ten times more powerful when you finally return to the minor tonality—the place where, in the words of Tom Morello (also a master of this concept), “true heaviness lives.”