Sandstone (Greywacke/Siltstone variant)

Physical Properties

Hardness: 6-7 (if silica-rich); Color: Grey, tan, earthy brown; Luster: Dull/Earthy; Crystal structure: Clastic/Granular; Cleavage: None (conchoidal to uneven fracture); Specific gravity: 2.2–2.8

Formation & Geological History

Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments. This specific rounded specimen likely originated in a high-energy fluvial (river) or glacial environment where erosion smoothed its edges over thousands of years.

Uses & Applications

Common varieties are used in construction (crushed stone), decorative landscaping, and historically as building stone or grindstones.

Geological Facts

Sandstone contains about 20% of all sedimentary rocks on Earth. The rounded 'cobble' or 'pebble' shape of this piece indicates it has traveled far from its source, likely tumbled by water or ice.

Field Identification & Locations

Identify by its gritty texture (feels like sandpaper when rubbed) and visible grains. Often found in riverbeds, glacial tills, and coastal areas. It is a fundamental rock for understanding regional depositional history.

Identified on: 4/18/2026

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