Obsidian
With a single blow from the hammer stone he chipped off a good sized blank. Half as long as his palm, two fingers wide and less than a finger in depth. He chipped at the edges with small blows. Shaping the stone. Each blow separating a small flake. The black surface of the stone reflecting light like water in a pond. He took a small piece of antler and pressure flaked the stone. He pressed the stone against the hide laid across his thigh. He shaped it. He gave it form.
The stone came from far away. More than two days walk, and across the river. But the stone around here did not break like this. This stone was magic. This stone would make an edge that cut hide easily. And when made into an arrow head, this stone would mean that he and his mate would not be hungry this winter. This stone would bring down the elk and feed them many days. And with the food the little ones would not die like last winter. And the hides would keep them warm.
There was magic in the stone, if he could bring it out.