sedimentary
Limestone Pebble
Calcite-rich Sedimentary Rock (CaCO3)
Hardness: 3 on Mohs scale. Color: Off-white to light tan. Luster: Dull, earthy. Crystal Structure: Microcrystalline calcite. Cleavage: Perfect rhombohedral in calcite crystals, though rarely visible in microcrystalline limestone nodules.
- Hardness
- 3 on Mohs scale
- Color
- Off-white to light tan
- Luster
- Dull, earthy
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Physical properties
Hardness: 3 on Mohs scale. Color: Off-white to light tan. Luster: Dull, earthy. Crystal Structure: Microcrystalline calcite. Cleavage: Perfect rhombohedral in calcite crystals, though rarely visible in microcrystalline limestone nodules.
Formation & geological history
Formed primarily in shallow marine environments through the accumulation and compaction of organic debris such as shell fragments, coral, and calcium carbonate precipitates over millions of years. Commonly stream-rounded or weathered by river erosion.
Uses & applications
Limestone is widely used in construction as aggregate, in cement production, soil conditioning in agriculture, and neutralizer in chemical processes. Small weathered pebbles are collected as landscaping stones.
Geological facts
Limestone makes up about 10% of total sedimentary rock volume on Earth. It reacts vigorously with dilute acids like vinegar, releasing carbon dioxide gas bubbles, which is a classic test for calcium carbonate rocks.
Field identification & locations
Field identification involves checking for hardness (can be scratched with a copper penny or steel knife) and testing with dilute acid (effervesces). Commonly found along riverbeds, beaches, and limestone karst landscapes worldwide.
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