sedimentary
Lignite (Brown Coal)
Humic Lignite (Carbonaceous sedimentary rock)
Hardness: 2.5–3.5 on Mohs scale; Color: Dark brown to black; Luster: Dull to earthy; Crystal Structure: Amorphous (non-crystalline); Cleavage: None/Irregular; Specific Gravity: 0.5–1.5 (relatively lightweight)
- Hardness
- 2
- Color
- Dark brown to black
- Luster
- Dull to earthy
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Physical properties
Hardness: 2.5–3.5 on Mohs scale; Color: Dark brown to black; Luster: Dull to earthy; Crystal Structure: Amorphous (non-crystalline); Cleavage: None/Irregular; Specific Gravity: 0.5–1.5 (relatively lightweight)
Formation & geological history
Formed from the compression of peat under relatively low heat and pressure. It is considered the lowest rank of coal and represents the transition from peat to bituminous coal. Typically dates from the Tertiary or Cretaceous periods.
Uses & applications
Primarily used as fuel for steam-electric power generation; occasionally used as a source of montan wax or for soil amendments in horticulture due to its organic content.
Geological facts
Lignite is often called 'brown coal' and still contains visible plant structures or 'woody' textures. It has a high moisture content (up to 45%) which makes it less efficient and more polluting to burn than higher-grade coals.
Field identification & locations
Identify by its brownish-black color, relatively light weight, and the presence of visible fossilized organic fibers or wood grain. It is commonly found in large deposits in Germany, North Dakota (USA), Australia, and Russia. Collectors value specimens that clearly show fossilized wood structures.
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