How to identify Coprolite

To correctly identify Coprolite (Fossilized feces), 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, ranging from black, brown, gray, tan, to reddish-brown, depending on the mineral composition (e.g., iron oxides for reddish hues, phosphate for grays).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, sometimes waxy if highly phosphatized or silicified.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Often smooth to slightly granular on the exterior, but can be rough or lumpy. Internal texture may reveal inclusions of bone, plant matter, or other undigested food items. Can exhibit spiral or coiled structures.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous or cryptocrystalline, as it is a fossilized organic material rather than a true mineral with a defined crystal structure. The mineralizing agents (e.g., apatite, quartz) may be microcrystalline.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is not a crystalline mineral.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in sedimentary rock formations, particularly those deposited in aquatic or semi-aquatic environments (e.g., lakebeds, river deltas, shallow marine settings) where rapid burial and anoxic conditions favored preservation. Common in shales, siltstones, sandstones, and phosphatic beds.

Key Facts

Hardness

Variable, typically 3 to 5 on the Mohs scale, depending on the degree and type of mineralization (e.g., higher if silicified, lower if primarily phosphatic).

Specific Gravity

Variable, typically 2.0 to 3.0, depending on mineral composition. Phosphatic coprolites are generally denser.

Crystal System

Amorphous (no crystal system, as it is a fossilized organic material). The mineral components may be cryptocrystalline.

Color

Black, brown, gray, tan, reddish-brown.

Luster

Dull, earthy, sometimes waxy.

Transparency

Opaque.

Fracture

Conchoidal to irregular, depending on composition and degree of mineralization.

Cleavage

None.

Composition

Primarily calcium phosphate (apatite group minerals), often with varying amounts of silica (quartz/chalcedony), calcite, iron oxides, and residual organic matter. The exact composition reflects the original fecal matter and the diagenetic environment.

Physical characteristics

• Crystal Habit: Not applicable; amorphous or cryptocrystalline aggregates of minerals.
• Cleavage Type: None.
• Fracture Type: Conchoidal to irregular.
• Tenacity: Brittle.
• Luster Type: Dull to earthy, sometimes waxy.

Explore Coprolite