sedimentary
Limestone with Chert or Siltstone bands
Sedimentary carbonate rock (CaCO3) often with siliceous impurities
Hardness: 3-4 (matrix) to 7 (siliceous areas); Color: Light grey, tan, buff with iron staining (yellowish-brown); Luster: Dull to earthy; Crystal Structure: Microcrystalline; Cleavage: None, often shows conchoidal or irregular fracture; Specific Gravity: 2.5-2.7
- Hardness
- 3-4 (matrix) to 7 (siliceous areas)
- Color
- Light grey, tan, buff with iron staining (yellowish-brown)
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (matrix) to 7 (siliceous areas); Color: Light grey, tan, buff with iron staining (yellowish-brown); Luster: Dull to earthy; Crystal Structure: Microcrystalline; Cleavage: None, often shows conchoidal or irregular fracture; Specific Gravity: 2.5-2.7
Formation & geological history
Formed by the accumulation of organic remains or chemical precipitation in marine or lacustrine environments. This specimen shows angular fractures and weathering characteristic of Paleozoic to Cenozoic terrestrial or shallow marine sedimentary deposits.
Uses & applications
Commonly used in construction as aggregate, in cement manufacturing, and as building stone. If high in silica, it may have been historically used for tool making.
Geological facts
Limestone is the primary source of lime used to neutralize soil acidity in agriculture. The brownish-yellow patches on this specimen are likely caused by the oxidation of iron-bearing minerals like goethite or limonite.
Field identification & locations
Identify in the field by testing with cold dilute hydrochloric acid (it will fizz). Look for bedding planes and angular fracture. Found globally in thick sequences across continents. Collectors value large, well-formed fossils if present.
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