Talc - talcum powder (King George's Park: SW18 4)

Probably about half a 25kg bag. I use it for sculpture projects and have kept the other half of the bag that I'm still using slowly.

https://polymer-additives.specialchem.com/product/a-elementis-finntalc-m30

"Finntalc M30 by Elementis is a coarse, lamellar, floated talc based on hydrated magnesium silicate. It is also used as a functional extender. It is pure, lamellar, very hydrophobic, inert and soft grade with stable color.

It effectively addresses challenges related to dimensional stability, reproducibility, consistent quality, flow behavior, and optimizes injection molding, extrusion, compounding processes and others.
It is ideal for various applications, including recycled plastics, automotive cabin and under the hood, household appliances, light-duty equipment, pipes, powdering, HVAC, packaging, profiles and furniture.
It is suitable for WPC, engineered plastics such as polyethylene (PE), polypropylene (PP), polystyrene (PS), TPO, TPE, and polyesters.
Finntalc M30 has a shelf life of 5 years."

It is more than 5 years old, but I've kept it dry inside a bag. It seems the same as new.