How to identify Belemnite

To correctly identify Belemnite (Belemnitida), 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

   Typically light to dark brown, grey, black, or yellowish, depending on the surrounding sediment and diagenesis.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy on the exterior; can be vitreous to pearly on fresh breaks, especially along crystal faces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly rough on the exterior. Freshly broken surfaces often show a radial fibrous texture.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not a mineral crystal, but a biogenic structure. The overall form is typically bullet-shaped, conical, or cylindrical. Internally, it's composed of microcrystalline calcite with a radial arrangement.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No true mineral cleavage, but can fracture conchoidally or irregularly, often revealing the radial fibrous structure.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in marine sedimentary rocks, particularly limestones, marls, shales, and chalks, deposited in shallow to deep marine environments. They are common in deposits from the Jurassic and Cretaceous periods.

Key Facts

Hardness

3-4 (Mohs scale) for the calcite guard, but can vary slightly due to diagenesis.

Specific Gravity

Approximately 2.7-2.9 g/cm³

Crystal System

Trigonal (calcite component)

Color

Brown, grey, black, yellowish

Luster

Dull to earthy (exterior), vitreous to pearly (fresh break)

Transparency

Opaque

Fracture

Conchoidal to irregular, often revealing radial fibrous structure

Cleavage

None (as a fossil structure), but the constituent calcite has perfect rhombohedral cleavage

Composition

Calcium carbonate (CaCO₃) in the form of calcite

Physical characteristics

• Crystal Habit: Not a mineral, but a biogenic structure. The internal calcite is microcrystalline with a radial fibrous arrangement.
• Cleavage Type: None (as a fossil), but the constituent calcite exhibits perfect rhombohedral cleavage in three directions.
• Fracture Type: Conchoidal to irregular, often revealing the internal radial structure.
• Tenacity: Brittle
• Luster Type: Dull to earthy on the exterior; vitreous to pearly on fresh breaks.

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