This is described as a brooch on 1st Dibs (seller is Shreve, Crump & Low) but it appears to actually be a fur clip. Clips like these had two prongs, and though I can’t see that they were actually used on furs (as the prongs would have damaged the underlying hide), they can be used quite easily on coats or dresses or jackets. That is, if you wear pins.
This one is reported to be circa 1905, with approximately 12 carats of diamonds set in platinum. Maker is unknown.
This sells for USD$25,500.