Does oyster shell also serve as grit?

[SayChicken]

I was told by an employee of a feed store that I didn’t need grit if I offered oyster shell as it serves as both a calcium supplement and a source of grit. For those in the know, what is your opinion?

 

[TooCheep]

Absolutely not. Grit is hard enough to grind food- in other words rocks. Calcium sources break down far easier so that they chicken can absorb it and use them for their own skeletons and for shells.

 

[Folly's place]

Folks at feed stores often have no idea what they are talking about! Grit and oyster shell are two different things, both essential.
Mary