Spiney Oyster Heishi with Coral

Same trip as the worry beads! BTW this was at ARC. Found this cute little heishi necklace as well for 1.99.

It has sterling beads in between the spiney oyster shell...at least I think that's what the shell is. It has a non-sterling barrel clasp. It measures 16". I don't know much about branch coral, but am presuming this is coral. I don't know for sure. Would someone bother using imitation coral in a necklace like this?

Is this spiney oyster shell or something else? Could it be real coral and is there a way to tell?

Thanks for looking!