whinstone

Below this mass lies a pale red hardened sandstone, and beneath that a trap-like whinstone.

The result was an intermediate substance, neither glass nor whinstone—a sort of slag.

In a short time we arrived at a pretty large river, called Boki, which we forded; it ran smooth and clear over a bed of whinstone.

Fire flew from the smitten blue whinstone where the point, with all the weight of his young body behind it, impinged on the wall.