metamorphic
Anthracite Coal
Anthracite (Carbon-based organic sedimentary rock transitioned to metamorphic)
Hardness: 2.5–3.0 on Mohs scale; Color: Black to dark steel-gray; Luster: Submetallic, vitreous, or brilliant; Crystal Structure: Amorphous (non-crystalline); Cleavage: Uneven or conchoidal fracture; Specific gravity: 1.3–1.8.
- Hardness
- 2
- Color
- Black to dark steel-gray
- Luster
- Submetallic, vitreous, or brilliant
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Physical properties
Hardness: 2.5–3.0 on Mohs scale; Color: Black to dark steel-gray; Luster: Submetallic, vitreous, or brilliant; Crystal Structure: Amorphous (non-crystalline); Cleavage: Uneven or conchoidal fracture; Specific gravity: 1.3–1.8.
Formation & geological history
Formed through the regional metamorphism of bituminous coal. Intense pressure and heat over millions of years (often Carboniferous period, approx. 300 million years ago) drive off volatiles and water, resulting in the highest carbon content (86–97%) of all coals.
Uses & applications
Primary use as high-grade fuel for domestic and industrial heating because it burns with a hot, clean blue flame with little smoke. Also used in water filtration (media), steel production, and as a starting material for synthetic graphite.
Geological facts
Anthracite is often called 'hard coal' or 'black diamond.' Because it has the lowest level of impurities and the highest energy density of all coal types, it is the most expensive and cleanest-burning coal available.
Field identification & locations
Identify in the field by its distinct submetallic sheen and high hardness compared to other coals (it will not soil fingers easily). Found in folded mountain belts like the Appalachian Mountains in Pennsylvania, USA, South Wales in the UK, and parts of China and Russia.
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