Pertaining to or having the nature of fire; containing fire; resembling fire. / (geology) Resulting from, or produced by, great heat. With rocks, it could also mean formed from lava or magma.

(geology) one of the major groups of rock that makes up the crust of the Earth; formed by the cooling of molten rock, either below the surface (intrusive) or on the surface (extrusive)

plural of igneous rock

In an igneous manner.

(rare) The quality or condition of being igneous.