OHMYGOSH THAT'S SO COOL! Where? Was it in Canada? They've got some sweet cratonic continental shield crust up there. Was it a gneiss? Was it a nice gneiss? I bet it was super-metamorphosed!
I was about to say the same thing, in reply to SiuiS. Language is made by people, and constantly changed by people, and that's what it's for. We use it for what we need words for right now, and words drop out and come in and change meaning, sometimes over and over again. Since "dude", "guy" and especially "man" are primarily used to mean "male (likely teen or older) human", that's what they mean now. It doesn't matter if (hypothetically) "man" originally meant "the girliest female girl-woman you ever saw doing womanly girl things" and was applied ironically, or spread out and got applied elsewhere. It means what it means now.
I would be happy if "man" and "men" became gender neutral and people used "were" and "wif" or "wer" and "wo" or whatever prefixes or suffixes they liked. But unless almost everyone uses "man" to mean "person" and almost everyone uses the other markers, until then it's gendered male as default. And it's the same, except less hypothetical, with "dude" (and "guys"). Since most people use and understand it to mean "male person", that's what it means. You can't fully use it in a gender-neutral way, since your audience is quite likely to be interpreting it as meaning a male person. I mean, you can use it any way you like, but unless you make it clear, other people aren't going to assume the less prevalent meaning.
Asta, don't you dare make me have to make you another card!
*hugs* Feel better and look after yourself.