1.
mudstone
A fine-grained sedimentary rock formed from hardened mud — a mixture of clay and silt particles deposited in still water such as lakes or the deep sea. Often contains fossils and, in some regions, petroleum or natural gas.
この地層は泥岩でできている。
This stratum is made of mudstone.
泥岩から貝の化石が見つかった。
Shell fossils were found in the mudstone.
泥岩は水を含むと崩れやすくなる。
Mudstone becomes prone to crumbling when it absorbs water.
この山の斜面は泥岩が多く、雨のあとは地滑りに注意が必要だ。
The slopes of this mountain have a lot of mudstone, so after rain one needs to watch out for landslides.
Composed of 泥 (mud) and 岩 (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:
- 泥岩層: mudstone layer / stratum
- 泥岩からなる: to consist of mudstone
- 化石を含む泥岩: fossil-bearing mudstone
- 黒色泥岩: black mudstone (often rich in organic matter)
- 泥岩が風化する: mudstone weathers / erodes
SIMILAR WORDS:
- 砂岩: sandstone — made of sand-sized grains; coarser than 泥岩
- 礫岩: conglomerate — made of rounded pebbles cemented together
- 頁岩: shale — a fissile (easily splitting) variety of mudstone; often grouped with 泥岩
- 粘板岩: slate — a low-grade metamorphic rock formed from shale or mudstone
- 堆積岩: sedimentary rock — the broader category that 泥岩 belongs to