Sandstone (River Rock)

Physical Properties

Hardness: 6-7 (on Mohs scale); Color: Tan, buff, and cream with dark grey/black mineral staining or lichen; Luster: Dull/Earthy; Crystal structure: Clastic (granular texture); Cleavage: None; Specific gravity: 2.2-2.8

Formation & Geological History

Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments over millions of years. This specific specimen shows signs of fluvial erosion (river rounding) and secondary mineral coating (desert varnish or manganese oxides).

Uses & Applications

Used extensively in construction for paving and walling. As a 'river rock,' it is popular in landscaping and decorative masonry.

Geological Facts

Sandstone makes up about 20% of all sedimentary rocks on Earth. The dark coloring on the surface is likely Manganese or Iron oxide staining, often referred to as 'desert varnish' when found in arid environments.

Field Identification & Locations

Identify in the field by its gritty, sandpaper-like texture and visible sand grains. These rounded 'cobbles' are commonly found in ancient or modern riverbeds and glacial outwash plains.

Identified on: 4/23/2026

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