sedimentary
River Stone (Limestone)
Sedimentary Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale), Color: tan to creamy beige, Luster: dull to waxy when wet, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture possible)
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Physical properties
Hardness: 3 (Mohs scale), Color: tan to creamy beige, Luster: dull to waxy when wet, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture possible)
Formation & geological history
Formed by the accumulation of shells, coral, algal, and fecal debris in clear, warm, shallow marine waters. This specific specimen has been rounded and smoothed by water erosion in a river environment.
Uses & applications
Commonly used as decorative garden stones, in construction aggregate, as a source for lime in cement, and occasionally for lapidary tumbling for beginners.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Because it is composed of calcium carbonate, it will fizz if a drop of weak acid (like vinegar) is applied to it.
Field identification & locations
Identify in the field by its soft texture, reactivity to acid, and presence in riverbeds. It is found globally in areas that were once prehistoric seafloors.
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