By Oxford English Dictionary literal definition, not all lubricants are fluids.

  Etiquette is a mere lubricant of the order of society. 

  Fine music‥has a sensible effect in‥animating and as it were, lubricating my inventive faculty.

Lube also used for cash - greasing palms, etc.

> The new approach relies on a layered form of manganese oxide—a mineral material with the right size layers to allow ions to slip in and out and to differentiate rare earth elements.

Seems literal to me!

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

https://en.wikipedia.org/wiki/Talc#Uses

https://en.wikipedia.org/wiki/Graphite#Other_properties