mudstone « Back to Glossary IndexA rock made of primarily mud, i.e. particles smaller than sand (≤0.064 mm). Related Articles: 16 Energy and Mineral Resources5 Weathering, Erosion, and Sedimentary Rocks6 Metamorphic RocksGlossary: fissileGlossary: slate« Back to Glossary Index Author: Chris Associate Professor, Salt Lake Community College, Salt Lake City, Utah View all posts by Chris