Igneous connects to Sanskrit Agni, the fire god — the same PIE root for fire produced both the name of a deity and the scientific term for volcanic rock.
Relating to or produced by fire; in geology, denoting rock that has solidified from molten magma or lava.
From Latin igneus (fiery, of fire), from ignis (fire), from Proto-Indo-European *h₁égnis (fire). The geological sense was established in the 18th century as scientists classified rocks by their origin. Key roots: *h₁égnis (Proto-Indo-European: "fire").
The PIE root *h₁égnis (fire) connects English igneous to Sanskrit Agni, the Vedic god of fire who remains one of the most important deities in Hinduism. The same root gives us ignite, ignition, and the less common igniparous. The geological classification of rocks into igneous, sedimentary, and metamorphic — which every student learns — was not fully established until the late 18th century, when the Plutonists (who believed