The 'hierarchy' of ability scores is not necessarily fixed.
So, gathering what we more or less decided on for the pyrite:
5 HD for Wyrmling?
Breath Weapon 1 is acid (line or cone of corrosive gas). BW 2 - the disorientation gas?
Alignment - CE or CN (opposite of gold dragons)?
What'll be the theme? I kind of see a slowish, calm (almost regal) creature - with occasionally wild bouts of destructive activity. A silent imposter of the truly regal gold dragon. May actually rule some portion of the nearby lands in manners appropriate to a gold, but lash out at minor slights.
(fun wikipedia observation: it appears that pyrite can sometimes contain small amounts of gold, enough to be a valuable ore)