Worn by the Hogons ( Supreme Spiritual Leaders of the Dogon Tribe in Mali )
and their guardian assistants .. called benekesena .. who are the chief priests, spiritual figureheads and usually the oldest men in the village.
The stones, according to Dogon mythology, are covenant stones .. douge .. representing the bones ( and hence the power ) of the Lebe, the first Hogon.
A beautiful photograph of exactly this type of necklace and further details
of its use, can be seen on page 114 of Angela Fisher's book Africa Adorned ..
from where the above information was obtained, with grateful thanks.