sedimentary
Limestone Pebble
Calcite-rich Sedimentary Rock (CaCO3)
Hardness: 3 on Mohs scale; Color: Light gray to tan/beige; Luster: Dull, earthy; Grain size: Fine-grained (micritic); Cleavage: None visible in hand sample; Reaction: Effervesces readily in dilute hydrochloric acid (HCl)
- Hardness
- 3 on Mohs scale
- Color
- Light gray to tan/beige
- Luster
- Dull, earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Light gray to tan/beige; Luster: Dull, earthy; Grain size: Fine-grained (micritic); Cleavage: None visible in hand sample; Reaction: Effervesces readily in dilute hydrochloric acid (HCl)
Formation & geological history
Formed in shallow marine, lake, or evaporite environments from the accumulation of organic debris like shells, coral, and algal remains, or chemical precipitation of calcium carbonate over millions of years. Naturally rounded and smoothed by water action in streams, rivers, or along beaches.
Uses & applications
Limestone is extensively used in construction as crushed stone, concrete aggregate, flux stone in steel production, and raw material for manufacturing cement and lime. Small water-worn pebbles are commonly used in landscaping and aquariums.
Geological facts
Limestone accounts for about 10% of the total volume of all sedimentary rocks. Famous landforms around the world, such as karst landscapes and limestone caves filled with stalactites and stalagmites, are created by the dissolution of limestone by acidic groundwater.
Field identification & locations
Can be easily identified in the field by its softness (scratched by a steel nail) and strong fizzing reaction when exposed to cold dilute acid. Commonly found near ancient or present riverbeds, lake shores, marine coastal areas, and limestone bedrock outcrops.
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