@Crazy Horse Lady,
Sorry I missed your post! Your horse bust is gorgeous!
No, my horse head isn't marble, it's a yellowish gold metal with an applied verdigris patina. Since it's non-magnetic I'm guessing it may be bronze or copper. I removed it from the base and looked carefully at the underside, but didn't find a mark there either. Over the past 25 years I've spent more than I paid for it on books on animal sculpture and sculptors, (where I learned that sculptors who specialize in animal sculpture are called "animaliers"), metal horse books, bronzes of The Roman Bronze Works Foundry, etc., as well as using online appraisers and posting to every online forum on the subject I can find, but still no luck.
My main interest is not in it's value, but I'd dearly love to know who the artist is and whether there are more of his (or her) works out there somewhere!