metamorphic
Anthracite Coal
Anthracite (Carbon-rich metamorphic rock)
Hardness: 2.5-3.0 on Mohs scale; Color: Black to dark grey; Luster: Sub-metallic to vitreous (glassy); Crystal Structure: Amorphous; Cleavage: Conchoidal fracture; Specific Gravity: 1.3-1.8
- Hardness
- 2
- Color
- Black to dark grey
- Luster
- Sub-metallic to vitreous (glassy)
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 2.5-3.0 on Mohs scale; Color: Black to dark grey; Luster: Sub-metallic to vitreous (glassy); Crystal Structure: Amorphous; Cleavage: Conchoidal fracture; Specific Gravity: 1.3-1.8
Formation & geological history
Formed through the regional metamorphism of bituminous coal in sedimentary basins. It occurs during mountain-building processes where high heat and pressure drive off volatiles, leaving 86-97% carbon. Most dates to the Carboniferous period (300-360 million years ago).
Uses & applications
Primarily used for domestic heating, industrial metallurgy, and water filtration. In jewelry, it is sometimes used as a substitute for jet (though jet is softer and lighter).
Geological facts
Anthracite is the highest grade of coal and contains the highest energy density. Despite being 'coal', it is classified as a metamorphic rock because it has undergone significant structural change due to heat and pressure.
Field identification & locations
Identify in the field by its black, shiny appearance, relatively light weight compared to silicate rocks, and the fact that it does not soil fingers like softer coal. It is commonly found in the Appalachian mountains of Pennsylvania, USA, and parts of Wales/Vietnam.
More like this
