Powdery white block under wooden floor?

[1930’sReno]

First time poster here looking for some advice!

We are taking up a wooden floor over a porch to add insulation in a 1930’s house. Have discovered this under the floor boards and in between the joists in the rafters. Any ideas? We’ve had the artex tested for asbestos which came back negative but it got me worried what this might be?

 

[Tigercubrider]

looks like an old bar of soap?

 

[blup]

An old salt lick such as used for livestock.

Blup

 

[HERTS P&D]

Block of cocaine!

Andy