I have seen the bracelets (not necklaces), but never the process of cutting the beads into pieces.

Sorry!

PS
Of course it appears to be logical that broken, chipped or not-so-nice beads are used for the process. But I am not sure we do the Mauritanian train-of-thought justice, when suspecting what we would do. It is certainly not out of the question Mauritanians use completely nice and intact Morfias for their bracelets.

The "holy ghost" - so to speak - is (also) in the detail, is in every single of the many broken pieces of the bead. Imagine an expensive bottle of perfume - lacking a better visualisation - even when the bottle breaks, any single drop of the fragrance is enough to smell the flavour!

PPS
The key to understand a seemingly crazy process lies in the decodation of the bead's design, lies in the true meaning of the bead. Knowing it, it makes sense to break it apart, while each of it's then many drilled splinters remains to contains the spirit of the whole. That's not even as weird as it may sound first. Think about the relic worship during the middle ages and even today!