How to identify Fossilized Dinosaur Skull

To correctly identify Fossilized Dinosaur Skull (Fossilized bone (calcium phosphate)), 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

   Highly variable, typically shades of brown, black, gray, tan, red, or yellowish, depending on the mineralizing agents (e.g., iron oxides for reds/browns, carbonaceous material for blacks/grays, silica for lighter tones).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, sometimes waxy or vitreous if heavily silicified.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be smooth, porous, or rough, often retaining the original bone texture, sometimes with visible cellular or vascular structures. The surface may show evidence of weathering or erosion.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous to microcrystalline, replicating the original bone structure. No distinct macroscopic crystal forms are typically observed, though microscopic mineral crystals may be present within the bone matrix.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is a biogenic material that has undergone permineralization or replacement, not a true mineral with a defined crystal lattice and cleavage planes. It will fracture irregularly.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in sedimentary rock formations, particularly fluvial (river), lacustrine (lake), and deltaic deposits, as well as ancient floodplains and coastal environments. These environments facilitate rapid burial and subsequent fossilization. Common in sandstones, mudstones, shales, and sometimes limestones.

Key Facts

Hardness

Variable, typically 3-7 on the Mohs scale, depending on the degree and type of mineralization. Original bone is around 4-5, but silicified bone can be 6-7.

Specific Gravity

Variable, typically 2.0-3.0, depending on the degree of mineralization and the specific minerals involved. Original bone is around 1.9-2.1.

Crystal System

Amorphous to microcrystalline (for the mineralizing agents), replicating the original biogenic structure. Original bone is cryptocrystalline hydroxyapatite.

Color

Highly variable: browns, blacks, grays, reds, tans, yellows.

Luster

Dull, earthy, sometimes waxy or vitreous.

Transparency

Opaque.

Fracture

Irregular to conchoidal (if heavily silicified).

Cleavage

None.

Composition

Primarily calcium phosphate (Ca5(PO4)3(OH,F,Cl) - hydroxyapatite) replaced or permineralized by various minerals such as silica (SiO2), calcite (CaCO3), iron oxides (e.g., Fe2O3, FeO(OH)), or other silicates.

Physical characteristics

• Crystal Habit: Massive, amorphous, or microcrystalline, preserving the original bone morphology.
• Cleavage Type: None.
• Fracture Type: Irregular to conchoidal.
• Tenacity: Brittle.
• Luster Type: Dull, earthy, waxy, or vitreous.

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