... I'm in Florida, so of course, we have tons of limestone, since this IS the land of limestone, and where much of the limestone in the whole country comes from. Uh... it's not hard. So it threw me when you guys started talking about how hard limestone is...
Not sure if this helps but here is some more info on Limestone....
As a former broker and fabricator of architectural stone, a strong majority of projects along the eastern seaboard utilize Indiana limestone. In laymens terms, once you dig past a few feet of the surface/cull layers, the stone is made of small and tight or dense grains. The grain pattern, color, and hardness change as you quarry deeper in ground. (See color quarry charts, section views, & geological info by searching "Indiana Limestone Handbook." Many of the limestone stone quarries in Florida a large grain or large shell compacted with significantly more air pockets, whether visible or microscopic. The stone is much lighter than Indiana limestone and most FL pieces will crumble if exposed to northern freeze/thaw cycles.
B/R, David
