Ignition has that lovely paragraph about some fluorine based fuel leaking out of the truck that was transporting it* and going through the road surface and then through the half a meter of concrete and stone under the asphalt, alien style.
* the only way to move that fuel was in a refrigerated cistern... at a temp so low that the steel it was made of became brittle and cracked.
I think it's quoted in one of Derek Lowe's articles about fluorine compounds too.
Retcon: the Xenomorphs were a form of life based around fluorine chemistry, which provides a physically plausible mechanism for how their blood eats through anything.
Of course that breaks the idea of them incubating in humans, since their biochemistry would react explosively with ours, but that never made sense anyway.
* the only way to move that fuel was in a refrigerated cistern... at a temp so low that the steel it was made of became brittle and cracked.
I think it's quoted in one of Derek Lowe's articles about fluorine compounds too.