An um. Yeah no everyone knows and it's been said many times that the suna suna no mi (crocs fruit) was a logia type. I'd love for you argue you're way out of this one man.

Easy. Citation needed. :-p

By the way, I don't mind being wrong, but now I'm curious. If the Suna suna no mi was a Logia type, then why isn't the Gomu Gomu no Mi? As far as has been shown, Luffy is "made of rubber" -- Croc is "made of sand". So what's the difference?