metamorphic
Anthracite Coal
Anthracite (Carbon Content: 86%-97%)
Hardness: 2.5–3.0 on Mohs scale; Color: Jet black to dark steel gray; Luster: Sub-metallic to vitreous (glassy); Crystal Structure: Amorphous (non-crystalline); Cleavage: Conchoidal fracture; Specific Gravity: 1.3–1.8
- Hardness
- 2
- Color
- Jet black to dark steel gray
- Luster
- Sub-metallic to vitreous (glassy)
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Physical properties
Hardness: 2.5–3.0 on Mohs scale; Color: Jet black to dark steel gray; Luster: Sub-metallic to vitreous (glassy); 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 occurs when sedimentary coal layers are subjected to high pressure and temperature during tectonic movements, typically dating back to the Carboniferous period (300-360 million years ago).
Uses & applications
Primarily used as a high-grade fuel for domestic and industrial heating due to its high energy density and low impurity content. Also used in water filtration systems and as a pigment or decorative stone in some folk art.
Geological facts
Anthracite is the highest rank of coal and burns with a short, blue, smokeless flame. It is the cleanest-burning coal available. Although it is biologically derived from plant matter, it is classified as a metamorphic rock because of the intense geological changes it undergoes.
Field identification & locations
Identify in the field by its distinctive metallic sheen, hardness (it does not soil fingers like softer coal), and tendency to break into smooth, curved surfaces (conchoidal fracture). Commonly found in the Appalachian region of Pennsylvania, South Wales, and parts of China.
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