Is this rock safe for isopods?

[Mwewe]

I collected some rocks that had fallen from old sea cliffs surrounding a wetland. Some are very brittle and chalky (I can’t believe people build homes on top of this stuff). 

The cup contains the powder generated by having the rocks in a plastic bag (and maybe jumbled around for some time in my car and other places lol). 
 

If the rocks are safe, what’s the best way to clean them? They’re porous so maybe a vinegar bath to remove outer coat? These are rocks from underneath someone’s property that had fallen onto the trail below. 

 

[Mwewe]

Maybe it’s limestone? 

I just chucked a small chunk of the lighter ones in vinegar and it dissolved in seconds. 
Dr. Google says, “These mild acids can dissolve rocks that contain calcium carbonate. The lemon juice and vinegar should have bubbled or fizzed on the limestone, calcite, and chalk, which all contain calcium carbonate.” (Uwaterloo.ca)

It would seem its natural calcium, and these rocks appealed to me because they’re light and flat, and might make nice hides for isopods. 

 

[Allpet Roaches]

They should be fine. Rocks are generally safe unless they are part copper or have been sprayed with pesticides.