Led Zepplin was the original heavy metal group- Lead being, a heavy metal--and heavy metal is, more or less, blues with the shuffle ironed out, or, as some have called it, blues without soul. Still, there is plenty of controversy as to the nature of heavy metal. I submit, from the webpage Is Silver a Heavy Metal?



>Historically, There is no Consensus on a Scientifically Valid Definition of Heavy Metal

>"There is a tendency, unsupported by the facts, to assume that all so-called "heavy metals" and >their compounds have highly toxic or ecotoxic properties. This has no basis in chemical or >toxicological data. Thus, the term "heavy metals" is both meaningless and misleading."

>- John H. Duffus, The Edinburgh Centre for Toxicology, Scotland, "Pure and Applied Chemistry" >74, 793–807



>A few thoughts by Stephen J. Hawkes of Oregon State University, Department of Chemistry, >demonstrate an interesting perspective:

>"The metals that I have seen referred to as heavy metals comprise a block of all the metals in >Groups 3 to 16 that are in periods 4 and greater. This seems to be a definition that should be >generally useful. It may also be stated as the transition and post-transition metals. These acquired >the name heavy metals because they all have high densities, but the usefulness of the term is >related to their chemistry, not their density.


No mention of the E to D chord changes--