Fossilized Shark Tooth

Description

Fossilized shark teeth are the mineralized remains of the teeth of cartilaginous fish belonging to the class Chondrichthyes (sharks, rays, and chimaeras). They are among the most common vertebrate fossils due to the continuous shedding and replacement of teeth throughout a shark's life (a single shark can produce tens of thousands of teeth in its lifetime). These fossils vary widely in size, shape, and color, reflecting the diversity of shark species and the geological conditions of their fossilization. They typically consist of a crown (the visible part of the tooth) and a root (which anchored the tooth in the jaw). The crown is often covered in a hard, shiny enameloid layer, while the root is more porous.

How to Identify

Color

Highly variable, depending on the mineral composition of the surrounding sediment and the permineralization process. Common colors include black, gray, brown, tan, blue, green, and reddish-brown. The enameloid crown is often darker and shinier than the root.

Luster

Vitreous to sub-vitreous on the enameloid crown, dull to earthy on the root.

Texture

Smooth and hard on the enameloid crown, often slightly rougher or porous on the root. Serrations or cusps may be present along the cutting edges, depending on the species.

Crystal Form

Not a true crystal, but a biogenic structure. The overall shape is characteristic of a shark tooth, with a distinct crown and root. Shapes vary from triangular, lanceolate, or bladed to flattened or pavement-like.

Cleavage

None, as it is a biogenic structure, not a mineral with a defined crystal lattice.

Geological Environment

Marine sedimentary environments, particularly shallow marine shelf deposits, estuaries, and ancient riverbeds that once flowed into marine settings. Often found in unconsolidated sands, gravels, clays, and limestones.

Key Facts

• Hardness: 5-6 on Mohs scale (due to permineralization, primarily silica or phosphate minerals)
• Specific Gravity: 2.5-3.0 (variable depending on permineralizing minerals)
• Crystal System: Amorphous (biogenic structure, not a true crystal)
• Color: Highly variable, often black, gray, brown, tan, blue, green, or reddish-brown.
• Luster: Vitreous to sub-vitreous on the enameloid, dull to earthy on the root.
• Transparency: Opaque
• Fracture: Conchoidal to irregular, depending on the permineralizing material and original tooth structure.
• Cleavage: None
• Composition: Primarily calcium phosphate (original tooth material) replaced by or infused with silica (SiO2), calcite (CaCO3), or other phosphate minerals (e.g., francolite).

Quick Check

• Color: Variable (black, gray, brown, tan, blue, green, reddish-brown)
• Luster: Vitreous to sub-vitreous (crown), dull to earthy (root)
• Streak: White to light gray (if powdered, but generally not applicable for identification)

Physical Characteristics

• Crystal Habit: Not applicable (biogenic structure)
• Cleavage Type: None
• Fracture Type: Conchoidal to irregular
• Tenacity: Brittle
• Luster Type: Vitreous to dull

Formation

Shark teeth are composed primarily of dentin and enameloid, which are highly resistant to degradation. Upon the death of a shark, the teeth, being denser and more mineralized than other skeletal elements (which are cartilaginous and rarely fossilize), sink to the seafloor. They are then buried by sediments (sand, silt, clay, shell fragments). Over geological time, the organic components of the tooth decay, and the porous dentin is gradually replaced by minerals from the surrounding sediment, typically silica (quartz), calcite, or phosphate minerals (e.g., francolite). This permineralization process results in a fossilized tooth that retains the original morphology but has a different mineralogical composition and often a distinct color derived from the infilling minerals and surrounding matrix.

Usage

Primarily of scientific interest for paleontological research, providing insights into ancient marine ecosystems, shark evolution, and paleogeography. Also highly valued by collectors, used in jewelry, and as educational specimens.

Age Distribution

Ordovician to Recent (approximately 485 million years ago to present), with significant abundance from the Cretaceous to Neogene periods.

Where to Find

Finding Tips

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Scientific Classification

Mineral Class

Not a mineral, but a fossilized biogenic material

Group

Fossil

Crystal System

Amorphous

Chemical Formula

Variable, primarily Ca5(PO4)3(OH,F,Cl) (original apatite) replaced by or infused with SiO2, CaCO3, or other phosphate minerals.

Composition

Permineralized dentin and enameloid, typically composed of silica, calcite, or phosphate minerals replacing the original bioapatite.

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