Can You Identify The Material In This Pendant?

Hi folks. I wonder if anyone can help me please?

My girlfriend kindly gave me this pendant to wear and she tells me that it belonged to her father. Can anyone tell me what the white tooth-shaped material is please?

My girlfriend has forgotten where her father said it was from (he died some years ago), but does vaguely recall that he talked about it coming from the sea (deep) and also that is may have come from a shell.

The green vein running down most of the length of the pendant seems quite strange but it must surely serve as a clue to the material used?

The white section is about 5cm long and about 1cm maximum circumference (at the top where it joins the silver part).

Thank you in advance for any help.....

(This was originally posted in the the 'Buddhism' Topic area, but I wasn't getting many replies and was recommended to place it here instead).