Traditionally made from galena (PbS, aka lead sulfide), it's now usually made from charcoal or other carbon sources. Well, in countries that regulate health issues and lead poisoning.
Here in Morocco, it's still made from galena.
In souq, I've watched artisans grind up the shiny grey metal cubes, shredding them into a very fine black powder that's mixed with a secret liquid and poured into a small container shaped more or less like a perfume bottle. Check out the illustrations here (and, for that matter, the text, most of which is relevant to Morocco).
I'm on a one-Volunteer campaign to reduce tezolt use. I know it's a Sisyphean battle, given the power of tradition, but I'm working on it. Lead poisoning is serious, especially in children, and it's common here to put tezolt on babies' eyes. In their eyes! It's bad enough in the eyes of adult women, where its soft-tissue access gives it carte blanche into the bloodstream. But in babies?! In America, parents are required to strip and repaint entire houses that have old, lead-based paint in them, just in case your kid decides to lick the wall. And here, parents rub a 50% lead goo into their newborns' eyes.
With a stick.
About 50% longer than a toothpick, and about as big around as the bottom part of a golf tee, the tezolt applicator is a wooden stick that you coat with tezolt - lead - and then jab into your eye. With practice, women become adept at it, and learn to do it without making themselves cry. The lead still stings, of course, but they've accustomed themselves to that.
So I explain to my American friends that yes, tezolt is made from galena, which, yes, is 50% pure lead (Pb), and that's usually enough to keep *them* from using it. And we're all trying to explain it to the women in our communities, but... Tradition is a hard one to fight. People here still rub mud into babies' umbilical cords, to "help them heal". In a land where handwashing is ritualized to basically wetting the fingers, and where mud is viewed as antiseptic, yeah, we've got our work cut out for us. But this is one battle I'm not giving up.