Its hard to tell what wood is, especially if its a picture or short section like yours. I hope this doesn't come to blows Stu, but I suspect that it is indeed Rosewood. Walnut and Rosewood can look a lot alike, especially if its aged,and I am sure it is.
For me what gives it away is the stamp on the end of it. This is a common practice down in Central American where Rosewood grows.The tribes down there get a stipend for the wood I believe and the stamp tells you where and when it came from. I could be wrong of course, but I am betting that its Rosewood.
Got some sandpaper? You could sand a little off the end grain and the sweet smell should tell you right way if its Rosewood or Walnut. That was how Rosewood got its name...a very sweet smelling wood that lasts quite awhile after its cut.
Either way, its always nice to get wood...exotic or otherwise.
I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"