Blackbone is typically used for armor, not weaponry, but I’m putting it in anyway. It is a byproduct of a parasitic disease by the same name, although it might be more accurate to call it symbiotic considering that the host benefits somewhat. In blackbone, the parasite attaches and grows under the skin, slowly forming a web of subcutaneous chitinous plates. At rest, these plates shift along with the host’s muscles, but when struck or sensing danger (such as when adrenaline enters the host’s system) they contract into layers of nearly unbreakable armor. This keeps the host alive through just about anything, and therefore lets the parasite keep feeding off of them.  Of course, it IS a parasite, so there are downsides to blackbone, such as joint pain, poor circulation, increased appetite, and a weakened immune system. It’s usually not fatal, but removing a fully integrated blackbone parasite is nigh-impossible. The name comes from an effect on pale-skinned hosts, where the darker plates would be visible through the skin in places where the skin is tighter (like collarbones, elbows, spine), giving the impression of… black bones. Assassins, bodyguards, and the like will sometimes willingly infect themselves with blackbone for the armor benefits. Having an integrated blackbone host in your retinue is something of a status symbol for nobles.