Sedimentary
Limestone (Cliff Formation)
Limestone (predominantly CaCO3 as calcite)
Hardness: 3 (soft to moderate), Color: Typically white, gray, beige, or yellowish, Luster: Dull to earthy (can be waxy or vitreous if crystalline), Crystal Structure: Microcrystalline to macrocrystalline, often granular, Cleavage: Three directions of perfect cleavage (for calcite crystals within), Specific Gravity: 2.7…
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Physical properties
Hardness: 3 (soft to moderate), Color: Typically white, gray, beige, or yellowish, Luster: Dull to earthy (can be waxy or vitreous if crystalline), Crystal Structure: Microcrystalline to macrocrystalline, often granular, Cleavage: Three directions of perfect cleavage (for calcite crystals within), Specific Gravity: 2.71
Formation & geological history
Formed from the accumulation of marine organisms' shells and skeletons (calcium carbonate) over millions of years in shallow marine environments. Processes include biological deposition and chemical precipitation. The geological age of such coastal formations can vary widely, from Paleozoic to Cenozoic, depending on the specific location.
Uses & applications
Predominantly used for building materials (cement, concrete, aggregate), historical construction (e.g., cathedrals, ancient ruins), agricultural lime, and as a raw material in various industrial processes.
Geological facts
Limestone is a major constituent of many iconic geological features worldwide, including the White Cliffs of Dover, the karst landscapes of China, and the formations seen in the image. It is susceptible to chemical weathering, forming caves and karsts. It also plays a vital role in Earth's carbon cycle.
Field identification & locations
Identify in the field by its light color, bedding planes (layers), and reaction to acid (fizzing due to calcite content). Often found in marine sedimentary basins and uplifted coastal areas, such as the one pictured. Look for fossil inclusions as a definitive identifier. Collectors might look for interesting fossiliferous samples or well-formed calcite crystals within limestone vugs.
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