sedimentary

Red Mudstone (Siltstone)

Lutite (primarily Quartz and Clay minerals with Hematite)

Hardness: 3-4 (varies based on cementation); Color: Reddish-brown to maroon (due to iron oxide); Luster: Dull to earthy; Crystal structure: Non-crystalline/fine-grained; Cleavage: None, but may show bedding planes; Specific Gravity: 2.4-2.8

Hardness: 3-4 (varies based on cementation)
Color: Reddish-brown to maroon (due to iron oxide)
Luster: Dull to earthy

Identified April 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the lithification of fine-grained mud, silt, and clay particles settled in quiet water environments like floodplains, lakes, or deep marine areas. The red color indicates oxidation of iron (hematite) during formation, often in terrestrial settings.

Uses & applications

Used in the manufacturing of bricks, cement, and pottery. Occasionally used in landscaping or as a base material in road construction, though it is softer than other stones.

Geological facts

Mudstone makes up approximately 65% of all sedimentary rocks on Earth. The red variety is a classic indicator of 'Red Beds,' which geologists use to identify ancient continental environments.

Field identification & locations

Identify in the field by its very fine texture (grains too small to see with the naked eye) and its tendency to feel smoother than sandstone. It often breaks into blocky fragments rather than thin sheets like shale. Look for it in riverbeds or eroded cliffs.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone

Arenite (primarily SiO2)

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Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary