Part of speech: adjective
Pertaining to or formed by means of fire.
Usage examples "igneous":
Nevertheless, there would seem to be a limit to the thickness of stony masses formed even under such favourable circumstances, for the analogy of tertiary volcanic regions lends no countenance to the notion that sedimentary and igneous
rocks 25, 000, much less 45, 000 feet thick, like those of Wales, could originate while one and the same fauna should continue to people the earth. - "The Student's Elements of Geology",
Sir Charles Lyell.
When the igneous
rocks were thrown up to the surface of the earth, they brought various metals with them. - "Diggers in the Earth",
Eva March Tappan.
We infer that the igneous
rock when in a molten state was forced between the strata, much as a card may be pushed between the leaves of a closed book. - "The Elements of Geology",
William Harmon Norton.