How to identify Jet

To correctly identify Jet (Lignite (a variety of coal)), 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

   Uniformly deep black, sometimes with a very dark brown tint.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to waxy when polished; dull to greasy when unpolished.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth and fine-grained. When unpolished, it can feel slightly earthy or woody.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous; it does not form crystals. It is an organic material, not a mineral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. It exhibits a conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in marine or estuarine sedimentary rock sequences, often associated with shales, sandstones, and other coal seams. It forms from buried wood in anoxic conditions.

Key Facts

Hardness

2.5-4 on the Mohs scale

Specific Gravity

1.30-1.35 (unusually low for a gem material, indicating its organic origin)

Crystal System

Amorphous (non-crystalline)

Color

Deep black, sometimes with a very dark brown hue

Luster

Vitreous to waxy (polished), dull to greasy (unpolished)

Transparency

Opaque

Fracture

Conchoidal

Cleavage

None

Composition

Primarily carbon (C), with varying amounts of hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). It is a complex organic polymer derived from fossilized wood.

Physical characteristics

• Crystal Habit: Massive, amorphous
• Cleavage Type: None
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous (polished), dull to greasy (unpolished)

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