I looked it up again. The pendant is from the Pende tribe from Congo and probably made in the fifties when it was still a belgian colony.
Lots of belgians, working in the colony brought souvenirs(once in a while original pieces of art) back to their families while visiting them every couple of years. That's how these carvings ended up back here. They were made out of the hard pit of a fruit from the "muhafu"(canarium schweinfurthii). Other substances from the tree were also used for coloring raffia clothes.
Sculpting the pit was part of a tradition independant from the ivory and wooden masks, also worn as pendants. You can find more in "L'Art Pende" from L. de Sousberghe, 1958.

Best regards,
Hendrik