Spilite

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.