metamorphic
Anthracite Coal
Anthracite (Carbon-rich metamorphic coal)
Hardness: 2.5–3.0 on Mohs scale; Color: Jet black to iron-black; Luster: Sub-metallic to vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; 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: 2.5–3.0 on Mohs scale; Color: Jet black to iron-black; Luster: Sub-metallic to vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Fracture: Conchoidal; Specific Gravity: 1.3–1.8
Formation & geological history
Formed through the low-grade metamorphism of bituminous coal. It involves high heat and pressure over millions of years (primarily during the Carboniferous period, approx. 300-360 million years ago) which drives off volatile matter and moisture, resulting in a high carbon content (86–98%).
Uses & applications
Primarily used as a high-grade fuel for domestic heating and industrial processes (smelting). It is also used in water filtration systems and, in polished form, for decorative jewelry or carvings (Jet is a similar organic gemstone).
Geological facts
Anthracite is the highest rank of coal and burns with a hot, clean blue flame with very little smoke or soot compared to other coal types. It is often referred to as 'hard coal' or 'black gold' in Pennsylvania, which holds most of the world's known supply.
Field identification & locations
Identify by its light weight relative to its size, deep black color, and the fact that it does not soil fingers like softer coal. Found in fold-mountain belts such as the Appalachians (USA), South Wales (UK), and parts of China. Collectors look for pieces with 'peacock' iridescence.
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