Black Sabbath (1976) Symptom of the Universe

Off the Sabotage album Sabbath's hardest hitting album with brutal numbers such as Hole in the Sky driven by a hard driving guitar figure and a virtuoso solo from Tony Iommi.  It's the sudden descent into a flamenco guitar section at 4:13 mark that is breathtaking flawlessly slipping into a jazzy rock progression with Ozzy's vocals howling vocals keeping the consistency with the  scorchingly delivered sentiment.  It presents their experimental side of the 70s along with their pioneering classic metal sound mixing chugging rhythms; the shift into a delicate, pleasant summery atmosphere is pulled off and is a understated feat.