A new discovery that surf metal detectorists know well

Barberian

Concretions on rusted metals and slag. Somebody showed an old coin covered with concretions I believe on this board once.

https://www.msn.com/en-us/news/technology/industrial-waste-is-turning-into-a-new-type-of-rock-at-unprecedented-speed-new-study-finds/ar-AA1GTf04?ocid=msedgntp&pc=HCTS&cvid=9f9b9128f66c4215921ab41408c5d767&ei=52