Malachite

Malachite is a type of mineral considered extremely toxic and/or poisonous worldwide. Its trade is strictly prohibited and discouraged by governments and clerical organizations worldwide, even if its effects on the body are nebulous.

Also called Visionary Wave.

Pieces of it will appear (rain?) down on the material plane from The Wandering Shard, but it is different than the naturally occuring malachite (?)
Malachite, even the Wandering Shard kind, usually does not grow off bodies.

From Thallium

"This is information pertaining to your future under the Ruby Disciples. Please pay attention. Do not share this information with outside members, with the exception of employed mercenaries, such as your new allies. You will sign a binding contract upon your next visit to Nayora, which I hope to be soon." He pauses, looking up and down at both BugSaw and Trick. "The Wandering Shard is a gigantic body of anomalous malachite floating in the Astral Sea, trajectory unknown and unpredictable. It represents a major threat to the Material Plane. One of the missions entrusted to the Ruby Disciples is to quietly monitor and collect any shards that might have broken off from it. I believe you have witnessed the effects of some such shards." The unnatural forms of malachite, spreading like lichen. Bubbles rising from skin, like a foul inversion of growth. "The kobold population is currently believed to be colluding with the Cult of the Wandering Shard, desperate folk who believe in bringing about a New Dawn- embracing malachite to be the way forward for our world. Your report is worrying. We have no such descriptions in modern day."

From the Shardborn Angel

The Angel's blood looks to actually be liquid malachite, which... Shouldn't be a thing? It's a green liquid that keeps the green banded patters on its surface, so it's not just powdered malachite suspended in water.