sedimentary
Sandstone (Greywacke)
Sandstone (SiO2 enriched with lithic fragments)
Hardness: 6-7 (Mohs); Color: Grey-green to tan; Luster: Dull/Earthy; Crystal structure: Clastic (fine-grained); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
- Hardness
- 6-7 (Mohs)
- Color
- Grey-green to tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Grey-green to tan; Luster: Dull/Earthy; Crystal structure: Clastic (fine-grained); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.65.
Formation & geological history
Formed through the accumulation and lithification of sand-sized grains, often in high-energy marine or fluvial environments. This specimen shows signs of rounded weathering through water erosion (beach or river pebble).
Uses & applications
Used primarily in construction as crushed stone or fill; decorative use in landscaping and aquariums; historically used for grindstones.
Geological facts
Sandstone accounts for roughly 20 to 25 percent of all sedimentary rocks in the Earth's crust. It is a critical reservoir rock for groundwater and petroleum.
Field identification & locations
Identify in the field by its 'sandpaper' texture and visible small grains. Commonly found on beaches, riverbeds, and in arid desert formations. Collectors look for unique banding or rounding.
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