sedimentary
Limestone with Bitumen/Chert
Calcite (CaCO3) containing organic hydrocarbons
Hardness: 3 (Mohs scale) for the matrix; Color: Tan to pale brown with black inclusions; Luster: Dull to earthy; Crystal Structure: Trigonal/rhombohedral calcite; Cleavage: Perfect rhombohedral in calcite crystals.
- Hardness
- 3 (Mohs scale) for the matrix
- Color
- Tan to pale brown with black inclusions
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 (Mohs scale) for the matrix; Color: Tan to pale brown with black inclusions; Luster: Dull to earthy; Crystal Structure: Trigonal/rhombohedral calcite; Cleavage: Perfect rhombohedral in calcite crystals.
Formation & geological history
Formed in warm, shallow marine environments from the accumulation of shell, coral, and algal debris. The dark spots likely represent trapped organic matter or bitumen that matured under heat and pressure.
Uses & applications
Limestone is used extensively in construction (aggregate, cement) and agriculture. Bituminous limestone can be a source of hydrocarbons or used as an ornamental stone.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. When it contains organic bitumen, it can sometimes emit a faint oily odor when freshly broken or heated.
Field identification & locations
Identify in the field by its softness (scratches with a copper penny) and its effervescence (bubbling) when in contact with dilute hydrochloric acid. Commonly found in karst landscapes and coastal cliffs.
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