How to identify Lignite

To correctly identify Lignite (Lignite), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Light to dark brown, sometimes yellowish-brown or brownish-black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull, earthy, or sometimes waxy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Soft, friable, often porous, and can feel somewhat woody or fibrous. Visible plant fragments are common.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous; does not form crystals. Occurs as massive, earthy, or woody aggregates.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits irregular fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in swamps, bogs, and deltaic environments where abundant plant material accumulates in an anoxic (oxygen-deficient) setting, preventing complete decomposition. These environments are typically found in low-lying coastal plains, floodplains, and intermontane basins.

Key Facts

Hardness

1-2.5 (Mohs scale)

Specific Gravity

1.1-1.5 g/cm³ (variable due to moisture content)

Crystal System

Amorphous

Color

Brown, yellowish-brown, brownish-black

Luster

Dull, earthy, waxy

Transparency

Opaque

Fracture

Irregular, conchoidal (rarely), or woody

Cleavage

None

Composition

Primarily carbon (25-35% dry, ash-free), hydrogen, oxygen, nitrogen, sulfur, and significant moisture content (30-70%).

Physical characteristics

• Crystal Habit: Massive, earthy, woody
• Cleavage Type: None
• Fracture Type: Irregular, sometimes woody or sub-conchoidal
• Tenacity: Brittle, friable
• Luster Type: Dull, earthy, waxy

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