metamorphic
Anthracite Coal
Anthracite (Carbon-based organic sedimentary rock exposed to metamorphic heat/pressure; Chemical composition is approximately 86%–98% Carbon)
Hardness: 2.5–3.0 (Mohs scale); Color: Black or very dark gray; Luster: Submetallic, glossy, or vitreous; Crystal Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 1.3–1.8
- Hardness
- 2
- Color
- Black or very dark gray
- Luster
- Submetallic, glossy, or vitreous
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Physical properties
Hardness: 2.5–3.0 (Mohs scale); Color: Black or very dark gray; Luster: Submetallic, glossy, or vitreous; Crystal Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 1.3–1.8
Formation & geological history
Formed through the regional metamorphism of bituminous coal. It involves the subjection of peat and plant matter to intense pressure and heat over hundreds of millions of years (often dating back to the Carboniferous period, approx. 300-360 million years ago) which drives off volatiles and moisture.
Uses & applications
Primarily used as a high-grade fuel for domestic and industrial heating because it burns with a clean blue flame and high energy density. It is also used in water filtration systems and as a reducing agent in metallurgical processes.
Geological facts
Anthracite is the highest rank of coal and represents the final stage before coal turns into graphite. Unlike lower grades of coal, it is relatively clean to the touch and does not leave black soot on fingers as easily.
Field identification & locations
Identify it by its shiny, almost glass-like metallic luster and its tendency to break in curved, shell-like (conchoidal) patterns. It is much harder and denser than common 'soft' coal. Commonly found in the Appalachian region of Pennsylvania, USA, as well as parts of South Wales and China.
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