[Hextinium]

After looking up mining slurry densities limestone is 2.7x the density of water. Calcium carbonate (limestone) is also used for filler in some medications. I'm pretty sure its just limestone slurry.

[jaclaz]

It is more like that is a sort of drilling mud (bentonite possibly additioned with baryte ):

https://en.wikipedia.org/wiki/Bentonite

https://en.wikipedia.org/wiki/Drilling_mud

Bentonite is also used in medicine (dermatology).