How do I repair a glass cooker hob (glass top stove)?
This apparently is for a smooth glass top on a stove. GE sells them, perhaps others now. Traditionally, the word is that these are generally replaced when cracked. A small chip on the edge may not be worth replacing the top (which is EXPENSIVE from what I've heard) until that crack chooses to propagate. The problem is, heat stresses in glass tend to turn small cracks into big ones.

You might ask the manufacturer, but I'll bet a large sum of money they have no interest in repair anyway. They want to sell you a new top.

The first solution I would think of is a high temperature silicon caulk. You can buy it in a tube, and it does come in black. I don't know how much it hardens though.

If not that, I would look for a high temperature epoxy. You can get colorants for epoxy.