It kind of looks like ironwood to me. There are a bunch of tools that look something like that. If it's a rib tool for ceramics, then it was custom made by someone because that wood is really fancy. It could be any of the things mentioned previously, but my guess is that it's used for some kind of burnishing, maybe in leather. How thick is it? I've made rib tools for myself and have a few store bought ones as well. They're usually kind of ~1/4"ish thick, maybe 3/8" on bigger ones, and tend to have fairly sharp edges.

Yeah it's roughly 1" thick, 12" long and 5" wide. From what I've seen on google it's a (wine bottle holder which balances.)[https://s-media-cache-ak0.pinimg.com/236x/f3/f1/3b/f3f13b84b1a126104dc9bf67423a42ed--surfboard-bottle-holders.jpg]

having a piece of red sandalwood (zitan) already, I compared the grain and color, which undoubtedly is identical and quite unique.

I initially thought it was desert ironwood (because it sank in water), but I have quite a few pieces of it which look distinctly different in terms of grain and color. This wood is black with a red/purple shimmer under light with long distinguishable pores, whereas desert ironwood is orange/brown/black with practically invisible pores.

Btw ironwood just refers to a general variety of hardwoods that are particularly dense.