sedimentary
Ferruginous Conglomerate
Conglomerate with Iron-Oxide Matrix (SiO2 + Fe2O3/FeO(OH))
Hardness: 6-7 (clasts), 4-5 (matrix); Color: Dark brown, rusty red, and grey; Luster: Dull/Earthy; Structure: Clastic (coarse-grained); Cleavage: None (breaks across grains); Specific Gravity: 2.6 - 3.2 (varies by iron content)
- Hardness
- 6-7 (clasts), 4-5 (matrix)
- Color
- Dark brown, rusty red, and grey
- Luster
- Dull/Earthy
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (clasts), 4-5 (matrix); Color: Dark brown, rusty red, and grey; Luster: Dull/Earthy; Structure: Clastic (coarse-grained); Cleavage: None (breaks across grains); Specific Gravity: 2.6 - 3.2 (varies by iron content)
Formation & geological history
Formed in high-energy fluvial environments (rivers) or alluvial fans where rounded rock fragments are deposited and later cemented together by iron-rich groundwater precipitating minerals like hematite or goethite. Age ranges from Precambrian to Cenozoic depending on the local basin.
Uses & applications
Used primarily as low-grade construction aggregate, fill material in road building, or as a decorative stone in landscaping. Historically, some high-iron variants were prospected as minor iron ores.
Geological facts
Conglomerates are often called 'puddingstone' because the rounded clasts resemble fruit in a pudding. Because the clasts are rounded, they indicate the material was transported a significant distance by water before lithification.
Field identification & locations
Identify in the field by the 'concrete-like' appearance with large, rounded pebbles embedded in a finer, rusty-colored cement. Often found in ancient riverbeds or mountain foothills. It feels heavier than standard sandstone due to iron content.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone (Quartz-rich)
Arenite (SiO2)
sedimentary
Sandstone (with man-made markings)
Arenite (composed primarily of Quartz, SiO2)
sedimentary