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Anthracite is a hard, compact variety of coal that has a submetallic to metallic luster. It is the highest rank of coal, characterized by its high carbon content (typically 92-98% by weight), low volatile matter, and low moisture content. Its formation requires intense geological pressure and heat, making it less common than other coal types. It burns with a short, blue, smokeless flame and produces intense heat.
How to Identify
- Color
- Jet black to dark gray.
- Luster
- Bright, submetallic to metallic, often vitreous (glassy).
- Texture
- Smooth, hard, and brittle. Often exhibits conchoidal fracture.
- Crystal Form
- Amorphous (non-crystalline) or cryptocrystalline, though it is a rock, not a mineral in the strict sense. It does not form distinct crystals.
- Cleavage
- No true cleavage; exhibits conchoidal fracture.
- Geological Environment
- Typically found in highly folded and faulted sedimentary basins that have undergone significant tectonic compression and burial, leading to high-grade metamorphism of pre-existing lower-rank coals. Common in foreland basins adjacent to orogenic belts.
Key Facts
- Hardness: 2.5-2.75 on Mohs scale (relatively soft, but harder than lower-rank coals)
- Specific Gravity: 1.3-1.7 g/cm³ (denser than lower-rank coals)
- Crystal System: Amorphous (non-crystalline)
- Color: Jet black, sometimes with a slight brownish tint
- Luster: Submetallic to metallic, vitreous
- Transparency: Opaque
- Fracture: Conchoidal (shell-like, curved surfaces), brittle
- Cleavage: None (no true cleavage)
- Composition: Primarily carbon (92-98% fixed carbon), with minor amounts of volatile matter, moisture, and ash.
Quick Check
- Color: Jet black
- Luster: Bright, submetallic to metallic
- Streak: Black to brownish-black
Physical Characteristics
- Crystal Habit: Massive, amorphous; does not form distinct crystals.
- Cleavage Type: None
- Fracture Type: Conchoidal, brittle
- Tenacity: Brittle
- Luster Type: Submetallic to metallic, vitreous
Formation
Anthracite is the highest rank of coal, formed from peat through a process called coalification. This process involves increasing pressure and temperature over millions of years, typically associated with deep burial and tectonic deformation (e.g., mountain building). Peat first transforms into lignite, then sub-bituminous coal, then bituminous coal, and finally, under extreme conditions, into anthracite. The high temperatures and pressures drive off volatile components (water, methane, carbon dioxide), increasing the carbon content.
Usage
Historically and currently used as a premium domestic and industrial fuel due to its high energy content and clean-burning properties (low smoke and sulfur). Also used in metallurgical processes (e.g., as a reductant in iron ore smelting), water filtration, and as a component in some carbon products.
Age Distribution
Primarily Carboniferous (Pennsylvanian and Mississippian periods), but also found in other geological periods where conditions for coalification were met, such as the Permian and Mesozoic.
Where to Find
Pennsylvania, USA
The largest known anthracite reserves in the world are located in northeastern Pennsylvania, particularly in the Appalachian Basin. These deposits are primarily of Pennsylvanian age.
South Wales, UK
Significant anthracite deposits are found in the South Wales Coalfield, formed during the Carboniferous period under intense tectonic forces.
Donbas Basin, Ukraine/Russia
Extensive anthracite reserves are present in the Donets Basin, a major coal-producing region with Carboniferous-age deposits.
Vietnam
Quang Ninh province in northern Vietnam holds substantial anthracite reserves, primarily of Permian age.
China
Various regions in China, including Shanxi and Guizhou provinces, have significant anthracite resources.
Finding Tips
Geological Maps
Consult geological maps of regions known for coal deposits, specifically looking for areas marked with high-rank coal or areas that have experienced significant tectonic deformation and burial.
Outcrops and Mine Dumps
Look for outcrops in areas with known coal seams. Old mine dumps and spoil heaps from historical anthracite mining operations can also be good places to find samples.
Associated Rocks
Anthracite is typically found within sequences of sedimentary rocks, including sandstones, shales, and limestones, often in highly folded or faulted structures.
Safety Precautions
When exploring old mine sites, be extremely cautious of unstable ground, abandoned shafts, and hazardous gases. Always prioritize safety and obtain permission before entering private land or mining areas. Anthracite dust, like all coal dust, can be a respiratory irritant and is combustible.
Similar Rocks
Bituminous Coal
Bituminous Coal
Also known as: Soft Coal
Lignite
Lignite
Also known as: Brown Coal
Graphite
Graphite
Also known as: Plumbago, Black Lead
Scientific Classification
- Mineral Class
- Organic Mineraloid (though often referred to as a rock due to its aggregate nature)
- Group
- Coal (highest rank)
- Crystal System
- Amorphous
- Chemical Formula
- Complex hydrocarbon mixture, predominantly carbon (C)
- Composition
- 92-98% fixed carbon, <8% volatile matter, <5% moisture, <10% ash. Trace elements include sulfur, nitrogen, oxygen, and various inorganic impurities.
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