A large vintage natural razor hone or sharpening stone.

We are not experts in stone identification however we believe this stone may be to be a Scottish Tam O Shanter stone, also known as a Scotch hone, with the typical speckled surface.

This stone measures approximately 8⁵/₁₆ inches (210mm) long by 1⁷/₈" (48mm) wide by 1¹/₄" (32mm) deep

The top surface is reasonably flat with only a slight hollow but may benefit from a little flattening/dressing before use, please see images.

A few small chips to the base, please see images. 

The last image shows the stone with water on its surface.