Thread: Vintage rock ID

I recently got this razor stone without any indication of origin, but I haven't really seen anything similar here in the forum/hone wiki. I'd appreciate if the more experienced honers could help me identify it.

The size is about 4-5x1x1/3. While wet and lapped, the color is very dark background with slight violet/brownish hue that is more visible in broad daylight. The anthill pattern is grey when wet and when dry it reflects the light pretty well (when angling the stone, the pattern pops up almost white at some angles). Here's a pictures of it on a windowsill in broad daylight. First picture is wet taken at a 90 angle. Second is dry about 45 degree angle.