metamorphic
Anthracite Coal
Anthracite
Hardness: 2.5–3.0 on the Mohs scale. Color: Black to dark steel gray. Luster: Submetallic to vitreous (glassy). Crystal Structure: Amorphous. Specific Gravity: 1.3–1.8. It has a conchoidal fracture.
- Hardness
- 2
- Color
- Black to dark steel gray
- Luster
- Submetallic to vitreous (glassy)
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Physical properties
Hardness: 2.5–3.0 on the Mohs scale. Color: Black to dark steel gray. Luster: Submetallic to vitreous (glassy). Crystal Structure: Amorphous. Specific Gravity: 1.3–1.8. It has a conchoidal fracture.
Formation & geological history
Formed through the prograde metamorphism of bituminous coal. Intense pressure and heat over millions of years (often Carboniferous period) drive out moisture and volatile matter, leaving a high carbon content (86-98%).
Uses & applications
Historically used for residential and industrial heating due to its clean-burning properties. Today used in metallurgy, water filtration, and occasionally in jewelry (as jet) or as decorative 'black diamonds' for collectors.
Geological facts
Anthracite is the highest rank of coal. Unlike lower-grade coals, it is difficult to ignite but burns with a short, blue, smokeless flame. It accounts for only about 1% of global coal reserves.
Field identification & locations
Identify in the field by its high luster, lack of soot when handled compared to soft coal, and its relatively low density. It is commonly found in mountainous regions like the Appalachian Ridge-and-Valley province in Pennsylvania, USA.
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