How to identify Coprolite

To correctly identify Coprolite (Coprolite), 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 reds/browns, carbonaceous material for blacks) and the surrounding sediment.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, sometimes waxy if silicified, or vitreous if highly permineralized with quartz.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be smooth, granular, or rough, often reflecting the original texture of the fecal matter. May show internal structures like bone fragments, plant fibers, or scales. The exterior may exhibit striations or impressions from the digestive tract.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous to microcrystalline, as they are not true minerals but rather fossilized organic material replaced by minerals. No distinct crystal forms are typically observed.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as coprolites are not crystalline minerals. They typically exhibit irregular or conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in sedimentary rock formations, particularly those associated with ancient aquatic or terrestrial environments where rapid burial and mineralization were possible. Common in lakebeds, river deposits, marine shales, and ancient soil horizons (paleosols). Often found in association with other fossils from the same ecosystem.

Key Facts

Hardness

Variable, typically 3-7 on the Mohs scale, depending on the mineral composition (e.g., apatite ~5, silica ~7, calcite ~3).

Specific Gravity

Variable, typically 2.5-3.2, depending on mineral composition. Phosphatic coprolites tend to be denser.

Crystal System

Amorphous to microcrystalline (not a true mineral with a defined crystal system).

Color

Highly variable: black, brown, gray, tan, reddish-brown.

Luster

Dull, earthy, waxy, or vitreous.

Transparency

Opaque.

Fracture

Irregular to conchoidal.

Cleavage

None.

Composition

Primarily calcium phosphate (apatite), silica (quartz, chalcedony), or calcium carbonate (calcite), with varying amounts of organic carbon, iron oxides, and inclusions from the original diet.

Physical characteristics

• Crystal Habit: Not applicable; amorphous to microcrystalline aggregates.
• Cleavage Type: None.
• Fracture Type: Irregular to conchoidal.
• Tenacity: Brittle.
• Luster Type: Dull, earthy, waxy, or vitreous.

Explore Coprolite