The Cracked phenomenon

Disease.
What seperates disease from other widespread sicknesses? Well, I suppose it's just categorising. Something long term, significant, that affects your body. But sometimes you're simply ill, or magic afflicts you. So what makes the difference? I would suggest perspective at best, given the connection of all things. Magical afflictions, scarring plagues and flesh-eating parasites... let's not focus too much on the minutae.
There are a... well, a subspecies at this point, of humans. They're callously referred to as the Cracked, most of the time. They suffer from an unusual affliction, one not caused by ill winds, or germs, or small creatures, but by the presence of a very specific kind of corruption. Originally caused by an extraplanar material, this particular corruption seemingly affects visual recognition itself - seeing the source of the corruption causes anyone with eyes that access the typical spectrum of light to see unusual purple glittering. This same corruption obviously caused those seeing the material to covet it, because humans apparantly share 80% of their instincts with common birds.
By the time a civilisation with an understanding of science, or sense of any kind, discovered the humans that discovered the rock, it had been carved by unknown means into an idol, and placed at the center of their village. But the most clear sign of it's presence was the deformity around the upper face of the villagefolk, their skin having broken and cracked away, the flesh underneath raw and pulsating and - inexplicably - glimmering as though that flesh was formed of thousands of crushed gems, like the material itself. These people now bore the source of the corruption themselves, and the sight of their faces will steadily afflict onlookers.
Children born to the Cracked people are born healthy, and a band of Long Elves did actualy kidnap newborns from a few families at one point to see if they grew the strange disease as they aged - they did not, but the moral implications were enough to stop that practise. Today, the Cracked valley has been their home for a century, and each known exit has been blocked off to prevent them being seen. What is not common knowledge, however, is that no apparant maximum range of transmission has been discovered. Were someone to climb a nearby mountain and glance down, they may find an unexpected scratching at their eyes a few hours later...

Type

Magical