Buckskin is almost always chrome tanned. Unless it is specifically described otherwise (like German/oil tanned, brain tanned, or bark tanned), it is chrome tanned.
There apparently is some chrome tanned imitation brain tanned stuff. I somehow managed to get ahold of a couple of hides like this from Tandy (though not advertized that way) about ten years ago. They were screaming yellow, but they were soft, and "fuzzy" on the outside surface, as opposed to the normal shiny, rubbery surface of chrome tanned. It was really neat stuff. Haven't seen any like that since.