| The focus of their attention is ancient obsidian, a volcanic glass formed as an igneous rock. |
| Rhyolite, extrusive igneous rock that is the volcanic equivalent of granite. |
| Sill, also called sheet, flat intrusion of igneous rock that forms between preexisting layers of rock. |
| As an added bonus, the lava would simultaneously pave roads and sidewalks when it hardens into a glassy smooth surface of igneous rock. |
| The lava flow managed to spill over the cooled igneous rock but what little did was diverted away from the town. |
| A Maori warrior made his mere of greenstone, an igneous rock, and ground one side to a sharp edge. |
