Limestone (specifically Bituminous or Carbonaceous Limestone)

Physical Properties

Hardness: 3 (Mohs scale); Color: Dark gray to black; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture common); Specific gravity: 2.3-2.7

Formation & Geological History

Formed through the accumulation of organic remains, calcium carbonate from marine organisms, and chemical precipitation in shallow marine environments. Often dates from the Paleozoic to Mesozoic eras.

Uses & Applications

Used in the manufacturing of cement, as a soil conditioner in agriculture, as crushed stone for road construction, and for carbon sequestration research.

Geological Facts

Dark-colored limestones often contain trapped organic matter or bitumen. When struck with a hammer, some varieties release a characteristic 'oily' or sulfurous odor due to these organic impurities.

Field Identification & Locations

Identify in the field by its effervescence (fizzing) when exposed to dilute hydrochloric acid. Common in karst topography and sedimentary basins worldwide.

Identified on: 4/25/2026

Mode: Standard