metamorphic
Anthracite
Anthracite (Carbon-rich metamorphic coal)
Hardness: 2.5–3.0 on Mohs scale; Color: Black to dark steel gray; Luster: Submetallic, brilliant, or vitreous; Crystal structure: Amorphous; Fracture: Conchoidal; Density: 1.3–1.8 g/cm³
- Hardness
- 2
- Color
- Black to dark steel gray
- Luster
- Submetallic, brilliant, or vitreous
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Physical properties
Hardness: 2.5–3.0 on Mohs scale; Color: Black to dark steel gray; Luster: Submetallic, brilliant, or vitreous; Crystal structure: Amorphous; Fracture: Conchoidal; Density: 1.3–1.8 g/cm³
Formation & geological history
Formed through the regional metamorphism of bituminous coal in areas of intense tectonic activity. It takes millions of years to form as pressure and heat drive off moisture and volatile matter, leaving high carbon content. Most date to the Carboniferous period.
Uses & applications
Primarily used for high-grade domestic and industrial heating because it burns with a clean blue flame. Historically used for smelting iron and in water filtration systems.
Geological facts
Anthracite is the highest grade of coal, containing 86% to 98% carbon. It is often referred to as 'hard coal' and is much more rare than other coal types, making up only about 1% of global coal reserves.
Field identification & locations
Identify in the field by its high density compared to other coals, its bright metallic sheen, and its tendency not to soil the fingers when handled. It is commonly found in fold belts like the Appalachian Mountains in Pennsylvania.
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