sedimentary
Limestone (specifically Marl or Chalk)
Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale); Color: White, light gray; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (in bulk form); Specific Gravity: 2.3–2.7
- Hardness
- 3 (Mohs scale)
- Color
- White, light gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: White, light gray; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (in bulk form); Specific Gravity: 2.3–2.7
Formation & geological history
Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. This specific crumbly white specimen suggests a biological origin from marine microorganisms.
Uses & applications
Primarily used in construction (as aggregate), cement manufacturing, soil conditioning in agriculture, and as a precursor for quicklime.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is essential for the formation of cave systems through the process of chemical weathering by slightly acidic rainwater.
Field identification & locations
Identify in the field by its softness (can be scratched by a copper coin) and its energetic effervescence (bubbling) when a drop of weak acid like vinegar is applied. Commonly found in road beds as crushed gravel.
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