Earthbenders & Bone-bending (Fanon)
So before I start, this is just a bit of a rant/tangent about bone-bending and why it is not feasibly possible for an earth-bender to perform bone bending.
So I’ll start this off by saying, just because the bone contains calcium (which for all intents and purposes is a heavy metal), does not mean that an earth-bender can bend it.
Let me explain, because calcium is a heavy metal, you might argue that a metal-bender would be able to manipulate said heavy-metal. However, how Toph invented metal was by sensing the raw earth minerals in the metal using seismic sense. Bone does NOT contain those raw earth minerals, so the argument is not feasibly possible for an earth/metal-bender by any stretch of the imagination.
Now that is not to say bone-bending is not possible in universe, in fact it’s very possible, just not by an earth-bender.
Now I’m no biologist or anatomy expert, however, it takes a quick google search to get this information. Bone, is 31% water, meaning that it is plausible for a water-bender to be a bone-bender, especially if they know blood-bending.
However, why stop at blood and bone? Human skin contains 64% water and muscle and kidneys contain 79%. Genetic tissue also contains water, meaning a water-bender has the possibility of essentially start a slow and painful necrotic process while you’re still alive.
ATLA or even Korra would’ve been much more horrifying if water-benders could essentially become Mahito from JJK or Shigaraki from MHA.
Anyway, this is just my explanation for why earthbenders cannot bone bend, but waterbenders could. Just thought I’d share my thoughts.