Sedimentary Rock

Sandstone

Sandstone (lithified quartz arenite, arkose, graywacke, etc. depending on composition)

Luster: Dull to earthy

Identified August 28, 2025More sedimentary rock →

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Physical properties

Hardness: Varies greatly depending on the cementing material and grain composition, typically 3-7 on the Mohs scale. Color: Highly variable, often shades of gray, brown, tan, yellow, or red, depending on the mineral content and presence of iron oxides. Luster: Dull to earthy. Crystal structure: Not applicable, as it's a clastic sedimentary rock composed of fragments. Cleavage: Not applicable. Specific Gravity: Typically ranges from 2.2 to 2.8.

Formation & geological history

Sandstone forms from the lithification of sand, which consists of weathered grains of pre-existing rocks and minerals. These grains are transported by water, wind, or ice and deposited in layers in environments such as beaches, deserts, riverbeds, and deltas. Over time, as more layers accumulate, the overlying pressure compacts the sand, and mineral-rich waters percolate through, cementing the grains together (e.g., with silica, calcium carbonate, iron oxides, or clay minerals). Geological Age: Can range from very recent (Quaternary) to billions of years old (Precambrian), depending on the specific deposit.

Uses & applications

Construction (building stone, flagstones, veneers), manufacturing (abrasives, glass-making if high silica content), oil and gas reservoirs, and decorative uses.

Geological facts

Sandstone has been used for centuries in construction, famous examples include the Red Rocks Amphitheatre walls in Colorado and parts of the Pyramids of Giza. It is also a significant reservoir rock for oil and natural gas due to its porosity.

Field identification & locations

To identify in the field, look for a clastic texture where individual sand grains, typically 0.0625 to 2 mm in diameter, are visible to the naked eye. It often feels gritty to the touch. Sandstone may exhibit bedding planes, cross-bedding (indicating ancient current directions), or ripple marks. It is commonly found globally in areas with past or present sedimentary depositional environments, such as ancient shallow seas, lakes, rivers, and deserts. Tips for collectors: Look for samples with interesting colors, sedimentary structures, or fossil impressions.

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