Neptunism is an obsolete geological theory that proposed all rocks, including igneous rocks, were formed by the crystallization of minerals in the early Earth’s oceans. Although discredited by modern geology, Neptunism played a role in the development of geological thought and the understanding of rock formation processes.
Reference: Pancaldi, G. (1983). “Neptunism and the Neptunists: A Controversy in Eighteenth-Century German Geology.” History of Science, 21(2), 155-189.