Looks like petrified wood chips?

[Lavook]

Our class found these along the creek walls that border the school's property.  They look like large petrified wood chips, but we are wondering if you can tell us what they might be.  Part of the schools property is considered preserved wetlands.  This might be a reason these are here.

[jpc]

They look like calcite, and no, the rocks have nothing to do with t being a wetland preserve.  

[Aurelius]

I find chunks very much like these within highly fossiliferous toarcian limestone deposits near me. They aren't fossils, but I'd be interested to know how they formed.

[abyssunder]

Try to determine their hardness.