I've been offered a "lump" of sugar before, and it was not a single sugar crystal. When I hear "large grain of salt" I imagine something like this https://crystalverse.com/sodium-chloride-crystals/, quite different than a lump.

Those huge salt cubes are so fascinating! New side project added to the list...

That is absolutely brillant and will make a fantastic week-long father-daughter science project. Thanks.

Now back to figuring out something new for a 6-year old to program using Scratch...

I'm 37 and it's also going to make a great me-me project.

I usually use "a few bags of salt" to imply that I don't trust the source.

perhaps a "mountain of salt" in this case?

A pinch of salt

a highway road side storage yard of salt

Boulder?

A handful of salt