Spilite (from Greek: σπιλάς) is a fine-grained igneous rock, resulting particularly from alteration of oceanic basalt.
The term was introduced into the geological literature by Alexandre Brongniart in 1827.[1] Spilite is formed when basaltic lava reacts with seawater, or from hydrothermal alteration when seawater circulates through hot volcanic rocks.[2]
It is a metasomatic rock with a microscopic or very-fine grain size produced by hydrothermal alteration of basalt, and composed of albite or oligoclase, together with chlorite, epidote, calcite, and actinolite.[3] Spilite is veined by calcite or chalcedony, and vesicles and cavities are filled with secondary minerals.[2] It is generally classed with basalts, and it often retains many textural and structural features characteristic of basalt.[3]