metamorphic
Anthracite Coal
Anthracite (Carbon-rich metamorphic coal)
Hardness: 2.5–3 on Mohs scale; Color: Jet black to iron-black; Luster: Sub-metallic to vitreous (glassy); Structure: Amorphous/Non-crystalline; Fracture: Conchoidal (shell-like curves); Specific Gravity: 1.3–1.8.
- Hardness
- 2
- Color
- Jet black to iron-black
- Luster
- Sub-metallic to vitreous (glassy)
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Physical properties
Hardness: 2.5–3 on Mohs scale; Color: Jet black to iron-black; Luster: Sub-metallic to vitreous (glassy); Structure: Amorphous/Non-crystalline; Fracture: Conchoidal (shell-like curves); Specific Gravity: 1.3–1.8.
Formation & geological history
Formed through the regional metamorphism of bituminous coal. It involves the subjection of organic plant matter to intense heat and pressure over millions of years (primarily during the Carboniferous period), which drives off volatiles and water, leaving a high carbon content.
Uses & applications
Primarily used for high-grade domestic and industrial fuel due to its high energy density and low smoke production. It is also used in water filtration systems and as a pigment or for decorative carvings by hobbyists.
Geological facts
Anthracite is the highest rank of coal, containing 86% to 98% carbon. It burns with a short, blue, smokeless flame. It is often referred to as 'hard coal' compared to 'soft' bituminous coal. Historically, the Lehigh Valley in Pennsylvania was the primary source in the US.
Field identification & locations
Identify in the field by its distinct glossy, metallic-like shine and the way it breaks into smooth, curved surfaces (conchoidal fracture). It is much cleaner to touch than lower grades of coal and will not leave a heavy soot residue on hands. Found in folded mountain belts like the Appalachians.
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