How to identify Petrified Wood

To correctly identify Petrified Wood (Fossilized Wood), 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

   Extremely variable, ranging from white, gray, black, brown, red, orange, yellow, green, blue, to purple. Colors are often banded or mottled, reflecting the original wood grain and the presence of various trace elements.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to waxy, depending on the degree of silicification and the specific mineral replacing the wood.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly rough, often exhibiting the texture of bark or wood grain. Can be finely crystalline to cryptocrystalline.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pseudomorph after wood; retains the external and internal structure of the original tree, including growth rings, knots, and cellular details. Does not exhibit its own crystal habit.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is typically composed of cryptocrystalline quartz or chalcedony.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in sedimentary environments where rapid burial of plant material occurred, such as floodplains, volcanic ash deposits, and ancient riverbeds. Common in areas with past volcanic activity that provided silica-rich groundwater.

Key Facts

Hardness

6.5-7 on the Mohs scale (due to quartz composition)

Specific Gravity

2.60-2.65 (similar to quartz)

Crystal System

Trigonal (for the quartz component), but the overall form is a pseudomorph after wood.

Color

Highly variable, depending on trace elements (e.g., iron oxides for reds/browns, manganese for blacks/blues).

Luster

Vitreous to waxy.

Transparency

Opaque to translucent.

Fracture

Conchoidal to uneven.

Cleavage

None.

Composition

Primarily silicon dioxide (SiO2), often in the form of chalcedony or opal. Trace elements contribute to color.

Physical characteristics

• Crystal Habit: Pseudomorph after wood; retains the original macroscopic and microscopic structure of the plant material.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal to uneven, typical of quartz.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy) to waxy.

Explore Petrified Wood