sedimentary
Black Limestone with Calcite Veining
Bituminous Limestone (CaCO3 with Organic Carbon inclusions)
Hardness: 3-4 (Mohs scale); Color: Dark charcoal to black with white or translucent veins; Luster: Dull to sub-vitreous (waxy when polished); Crystal Structure: Rhombohedral (microcrystalline); Cleavage: Perfect rhombohedral in calcite veins; Specific Gravity: 2.3–2.7
- Hardness
- 3-4 (Mohs scale)
- Color
- Dark charcoal to black with white or translucent veins
- Luster
- Dull to sub-vitreous (waxy when polished)
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Physical properties
Hardness: 3-4 (Mohs scale); Color: Dark charcoal to black with white or translucent veins; Luster: Dull to sub-vitreous (waxy when polished); Crystal Structure: Rhombohedral (microcrystalline); Cleavage: Perfect rhombohedral in calcite veins; Specific Gravity: 2.3–2.7
Formation & geological history
Formed in marine environments through the accumulation of organic-rich calcium carbonate mud, which lithifies over millions of years. The white veins are formed by later tectonic stress or cooling, which causes fractures that are subsequently filled by precipitating calcite crystals from mineral-rich groundwater.
Uses & applications
Used primarily in decorative construction (tiles, countertops), landscape architecture, and as polished worry stones or decorative pebbles in water features.
Geological facts
Black limestone frequently contains high amounts of organic matter, which gives it its dark pigment. In some varieties, when scratched or struck with a hammer, it releases a faint smell of sulfur or bitumen (fossil organic matter).
Field identification & locations
Identify in the field by its dark color and high reactivity to dilute hydrochloric acid (it will fizz). Commonly found in the Carboniferous and Devonian rock layers of Europe (especially Ireland and Belgium) and the Midwestern United States. It is a common 'river rock' find in regions with ancient limestone bedrock.
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