Isn't Guns N' Roses heavy metal?

I recently purchased "Metal: The Definitive Guide" by Garry Sharpe-Young, and while it seems to be very well written and in-depth for the most part, it makes no mention of "Glam metal" bands like Guns N' Roses, Van Halen, etc. Are these not heavy metal bands of a different style?
Update: The answers pouring in so far seem to say no, but it seems that, in my research, most sources would say that Guns N' Roses are in fact metal, just a different splinter of the traditional heavy metal genre.
(I'm writing a research paper on heavy metal).
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