Quartzpike was a magically-infused plague that ravaged Acetate over a thousand years ago, killing a significant percentage of the Roner population and acting as the catalyst for the formation of the modern Navroyan state.
Origin
Quartzpike was created by a human noble as a weapon of assassination to be used in a coup for control of Bostra, the northern half of what would become Navroya. With the help of a demon, the noble empowered a naturally-occurring disease through many complex magical rituals. However, though his original intention was to create a weapon that would kill only closely related members of a specific family, his tenuous grasp on the magic he was wielding caused the disease to target not just them, but all Roner. The plague quickly grew out of hand and spread far and wide, causing the deaths of millions.
Symptoms
The disease turns the flesh of the victim to crystal resembling quartz slowly, from the bones outwards to the skin. Starting at the extremities, a victim's hands and feet would turn to hard, immobile crystal at about the time the disease begins to affect the torso and head. As it progresses, spikes of crystal would pierce through muscle and eventually skin, making it very painful to move. As it took several days for symptoms to even begin appearing, it was very difficult to quarantine, and led to a long and slow death.
Transmission
Foremost, by contact with the infected's crystal protrusions. This could be achieved by getting cut or wounded by crystals in living victims, or by the much more infamous second method.
After quartzpike killed its victim, their body would completely crystallize and turn into an almost unrecognizable mass of protruding shards sprouting out of the corpse. When anything came too near to one of these late-stage corpses, it would explode and send infectious crystal shards flying everywhere, embedding themselves in walls, ceilings, and bodies, thereby spreading the disease and contaminating the area thoroughly.