metamorphic
Anthracite Coal
Anthracite (Carbon-based metamorphic rock)
Hardness: 2.5–3 on Mohs scale; Color: Jet black to dark grey; Luster: Sub-metallic to brilliant/vitreous; Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 1.3–1.8
- Hardness
- 2
- Color
- Jet black to dark grey
- Luster
- Sub-metallic to brilliant/vitreous
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Physical properties
Hardness: 2.5–3 on Mohs scale; Color: Jet black to dark grey; Luster: Sub-metallic to brilliant/vitreous; Crystal structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific gravity: 1.3–1.8
Formation & geological history
Formed through the low-grade metamorphism of bituminous coal. It requires high pressure and temperatures (around 200–300°C) to drive off volatile matter and water, leaving behind high carbon content. Most anthracite was formed during the Carboniferous period, approximately 300 to 360 million years ago.
Uses & applications
Used primarily for heating and industrial fuel due to its high energy density and low smoke production. High-quality specimens are used in water filtration, and more rarely, carved into jewelry or collectibles.
Geological facts
Anthracite contains the highest percentage of carbon (86% to 98%) among all forms of coal. It burns with a short blue flame and is the cleanest-burning coal available.
Field identification & locations
Identify by its light weight (low density), deep black color, and the way it shatters like glass (conchoidal fracture). It will not rub off black soot onto your fingers as easily as softer coal types (bituminous). Often found in folded mountainous regions like Pennsylvania, USA.
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