Wait a second if you were to answer what type of fruit Marshall D. Teach has what would be your answer and why? I know I'm changing the subject but I just wanna see your reasoning in another character.
Sure thing. First look, it would spell Paramecia to me. A Logia is a fruit that allows the user to produce an element AND turn into the element itself. Some Paramecia were able to produce certain substances, not elements per se, but still close enough, like Wax and Poison, but were never able to turn into that substance. Others were able to turn into a substance in a way, like Rubber, where their body changes and molds and stretches, but their form would stay the same, and they wouldn't be able to produce the element outside their bodies. When Logia change their bodies, though, they can fully turn into their elements, they can be a flame, or ice, or light.
To me, Blackbeard would seem like a Paramecia, because his main exhibition of power is a black mist-like substance, which we associate with Dark, but his body would not turn into that substance, like our usual Logias. So it looked like Mr 3, or Magellan's DF. But his body did not behave like theirs. And so, as we saw him fight, we started to see that his body does turn and IS darkness, not the mist substance we see, but darkness nonetheless. We see it because his touch nullifies powers, we see that because, if he fails to catch attacks with his mist-substance, his body will absorb the attack (and damage him far greatly than it would another person), etc. He can't fly nor dodge like a normal Logia, but we can see he can't simply be a Paramecia either. So Oda's classification as Logia is correct. A very unusual Logia, but a Logia nonetheless.
Now you know my answer, I'll have yours. List me characteristics of a Logia type, and I'll correct you.