A little searching turns up that Italian marble pietra dura "specimen" rulers were a thing, popular in the late 1800s as Grand Tour souvenirs. This, however, is not that--it appears to be to be all one piece of marble, with carved lines to delineate inches and the variations in color done with some sort of dye. I tend to like aspirational things imitating other things, but what I especially like about this one, which makes it quite singular, is that someone hand-carved numbers down one side, with the style of those carved numbers making me believe it dates to the late 19th/early 20th century. And so it feels more akin to me to a folk art stone carved book than it does to Italian Grand Tour souvenir--and indeed it does its job as a ruler, measuring and marking 12 inches!

12” x 2” x 13/16” and in overall pretty good shape, with fading to the color and some extra carved marks here and there, which I think are to the good. The numbers are not so easy to pick up in photos, but they are very clear in person.