I've always had this problem with Naquadah: it is specifically described as an "element" in several places, yet it's not one we're familiar with. Well, the only ones we're unfamiliar with don't exist in nature. There's no room to slide any more in, either. (For those of you who don't know, "elements" are pure atoms, in their most basic form, not mixed with anything else. Each atom has a unique atomic number, i.e. the number of protons in its nucleus. We know the atomic weights of each naturally occurring element, from atomic number 1 (hydrogen) to 92 (uranium), in a straight sequence with no gaps. We've also been able to manufacture heavier elements in the lab (93-112; 114; 116; 118).
The thing is, the heavier elements are inherently unstable (i.e. radioactive). Intensely so; that's why uranium is used in atomic weapons and reactors. And the higher the atomic number, the more unstable and radioactive it is; the newest elements to be created/discovered only lasted a few seconds before decaying into lighter, stabler elements (giving off radiation in the process). Since the lighter elements are so well-known, any new element has to be higher than 112. Which means _highly_ unstable and radioactive. And this is the stuff they mine out of the ground with picks and axes, and make into everything? This is the stuff that Carter's got inside her? Why, I asked myself, didn't they all die of radiation poisoning?
At last, I have my answer. I was watching a program on the Science channel this morning about the most important scientific discoveries of 2004, and they started talking about the new elements discovered last year. In the conversation, they mentioned that scientists are fairly sure that once you hit an atomic number of 130 or so, the elements would start to be stable again. Why they believe that they didn't say.
But who cares! It solves the problem with Naquadah. Naquadah is indeed an element with a high atomic weight, probably somewhere in the 130's. That would also explain why pure naquadah is so heavy; it would have to be somewhere around twice the weight of lead. (Lead (Pb) has an atomic number of 82, a little over half that of what Naquadah would have to be.)
So I propose an addition to the Periodic Table . I think Nh would be a good symbol for it (Na is already taken; it's sodium). Though I could be persuaded to go with Nq. Whatcha think?