White Bricks in the attic?

In the attic of a 100 year old home I find all of these white bricks. They are light weight and feel and look like chalk. Any thoughts on what they are and why they would be in an attic? Especially an attic with only a 14 X 18 inch opening.

Maybe this:

Thank you David. These bricks come apart easily and in layers. They may be insulated fire brick and years have caused them to deteriorate.
I have a piece and hope to have a geologist look at it.

those are refractory bricks

Thanks Mark. Still wonder the benefit if storing them in an attic.