泥岩(でいがん)

Composed of 泥(でい) (mud) and 岩(がん) (rock). The reading uses the on'yomi でい, typical of technical rock names. Formed when mud — very fine clay and silt — is compacted and cemented over long periods into a solid rock.

Usage

Appears in geology and earth-science contexts: textbooks, geological survey reports, news about landslides, and discussions of oil and gas reservoirs (many source rocks for petroleum are mudstones). Japanese hillsides with mudstone layers are known for being slide-prone, so the word also appears in disaster-prevention reporting.

Common collocations

• 泥岩(でいがん)層(そう): mudstone layer / stratum
• 泥岩(でいがん)からなる: to consist of mudstone
• 化石(かせき)を含(ふく)む泥岩(でいがん): fossil-bearing mudstone
• 黒色(こくしょく)泥岩(でいがん): black mudstone (often rich in organic matter)
• 泥岩(でいがん)が風化(ふうか)する: mudstone weathers / erodes

Similar words

• 砂岩(さがん): sandstone — made of sand-sized grains; coarser than 泥岩(でいがん)
• 礫岩(れきがん): conglomerate — made of rounded pebbles cemented together
• 頁岩(けつがん): shale — a fissile (easily splitting) variety of mudstone; often grouped with 泥岩(でいがん)
• 粘板岩(ねんばんがん): slate — a low-grade metamorphic rock formed from shale or mudstone
• 堆積岩(たいせきがん): sedimentary rock — the broader category that 泥岩(でいがん) belongs to