noun
aqueous rock; sedimentary rock formed in water
Geological term for rock formed by deposition in water. In modern Japanese, 堆積岩 (たいせきがん) is more common for sedimentary rock in general, but 水成岩 specifically emphasizes formation in an aqueous environment.
この地域には水成岩が広く分布している。
Aqueous rocks are widely distributed in this region.
堆積岩 is the broader term for sedimentary rock, while 水成岩 specifically refers to rocks formed in water.
Compound of 水 (water) + 成 (become, form) + 岩 (rock). The term is a direct calque from Western geological terminology.