Where is Limestone found?
Limestone (sedimentary rock, primarily composed of calcite)
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Open the appLimestone occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Limestone
United States
Extensive deposits are found in the Appalachian Basin, Michigan Basin, Illinois Basin, and throughout the Great Plains and Rocky Mountains. Notable formations include the Mississippian-age limestones of the Midwest and the Cretaceous limestones of the Gulf Coast.
Europe
Significant limestone regions include the Paris Basin (France), the Jura Mountains (France/Switzerland), the Alps, and the extensive karst regions of the Mediterranean (e.g., Italy, Greece, Croatia).
Middle East
Large deposits are present in Saudi Arabia, Jordan, and Israel, forming significant parts of their geological landscapes.
China
Vast limestone formations are found across southern China, particularly known for their spectacular karst topography.
Collecting tips
- Acid Test. The most definitive field test for limestone is its reaction with dilute hydrochloric acid (HCl). Calcite (CaCO3) will effervesce vigorously, producing carbon dioxide gas. A 10% HCl solution is commonly used. Dolomite will react much less vigorously or only when powdered.
- Hardness Test. Calcite has a Mohs hardness of 3. It can be scratched by a copper coin (hardness ~3.5) but will scratch gypsum (hardness 2). This helps distinguish it from harder rocks like chert or quartz sandstone.
- Examine for Fossils. Many limestones are fossiliferous, containing visible shells, shell fragments, or other skeletal remains of marine organisms. This is a strong indicator of its biogenic origin.
- Look for Karst Topography. Limestone terrains often exhibit distinctive karst features such as sinkholes, caves, disappearing streams, and solutional weathering patterns due to its solubility in acidic groundwater.
Quick Check
- Color:
- White, gray, tan, buff (variable)
- Luster:
- Dull to earthy (fine-grained), vitreous to pearly (crystalline)
- Streak:
- White
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