coral or stone?

[i.amsherlocked]

Found washed out from a river bank in Northern Alberta.

[Pseudogygites]

Doesn't look like coral to me. The pits, or cells if it were a coral, are irregular in spacing and in size. They could be burrows or some kind of trace mark from bivalves, I suppose.

[Doctor Mud]

Looks like Tufa.

 

https://en.m.wikipedia.org/wiki/Tufa

 

we get a lot of this washing up on local beaches. Lots of it has casts of plant material and plant roots.
 

Can you see that any of those holes are the imprints of plant roots?

 

It can form in areas where there is calcerous bed rock. The rock is leached by groundwater forming a calcium carbonate solution.

this forms tufa when it emerges from the ground in springs.