How to identify Fossil

To correctly identify Fossil (Fossilized organism), 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, depending on the original organism and the mineralizing agents. Can be white, gray, black, brown, red, yellow, or even iridescent. Often matches the color of the surrounding matrix rock.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Variable, from dull to earthy (for carbonized remains or molds) to vitreous (for silicified fossils) or pearly (for some shell material).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Variable, reflecting the original organism's structure (e.g., bone, shell, wood grain, leaf venation) or the texture of the infilling/replacing mineral. Can be smooth, rough, porous, or crystalline.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable in the mineralogical sense for the fossil itself, as it represents an organism's structure. However, the replacing minerals may exhibit their characteristic crystal forms (e.g., quartz crystals in a geodized fossil).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable to the fossil as a whole. If the fossil is composed of a specific mineral (e.g., calcite), that mineral will exhibit its characteristic cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Predominantly found in sedimentary rocks formed in aquatic environments (marine, lacustrine, fluvial), such as limestones, shales, sandstones, and siltstones. Also found in volcanic ash deposits, amber, and rarely in glacial ice or permafrost.

Key Facts

Hardness

Highly variable, depending on the composition of the fossil and the replacing minerals. Can range from 1 (e.g., carbonized plant material) to 7 (e.g., silicified wood).

Specific Gravity

Highly variable, depending on the composition. Can range from ~1.5 (for carbonaceous fossils) to ~3.0 (for pyritized fossils) or higher.

Crystal System

Not applicable to the fossil as a whole, as it is an organic structure. The replacing minerals may have their own crystal systems (e.g., calcite is trigonal, quartz is trigonal).

Color

Variable, often shades of brown, gray, black, white, red, yellow.

Luster

Variable, from dull to earthy, vitreous, or pearly.

Transparency

Opaque to translucent, rarely transparent (e.g., some amber inclusions).

Fracture

Variable, depending on the material. Can be conchoidal (silicified), splintery (petrified wood), or irregular.

Cleavage

Not applicable to the fossil as a whole. If composed of a specific mineral, that mineral's cleavage will be present.

Composition

Extremely variable. Original organic material (e.g., chitin, cellulose, bone apatite, shell aragonite/calcite) often replaced or permineralized by inorganic minerals such as calcium carbonate (CaCO3), silica (SiO2), iron sulfides (FeS2), calcium phosphate (Ca5(PO4)3(OH,F,Cl)), or carbon (C).

Physical characteristics

• Crystal Habit: Not applicable; represents the morphology of the original organism.
• Cleavage Type: Not applicable to the fossil as a whole; depends on the mineral composition.
• Fracture Type: Variable (e.g., conchoidal, splintery, irregular).
• Tenacity: Variable (e.g., brittle, tough).
• Luster Type: Variable (e.g., dull, earthy, vitreous, pearly).

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