How to identify Petrified Wood

To correctly identify Petrified Wood (Silicified Wood (variety of Chalcedony/Quartz)), 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, depending on trace mineral impurities. Common colors include shades of brown, gray, black, red, orange, yellow, and sometimes blue or green. Often exhibits multiple colors in bands or patterns.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to waxy, depending on the specific type of silica (chalcedony or opal) and the polish.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly granular when broken, but the surface often retains the texture of the original wood, including bark patterns, wood grain, and growth rings. Can feel cool and hard to the touch.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Does not exhibit macroscopic crystal forms; it is a pseudomorph after wood. The silica itself is cryptocrystalline (chalcedony) or amorphous (opal).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None, as it is composed of cryptocrystalline quartz or opal.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Typically found in sedimentary environments where rapid burial of plant material occurred, often associated with volcanic ash falls, floodplains, ancient riverbeds, and lake deposits. Common in arid or semi-arid regions where erosion exposes ancient sedimentary layers.

Key Facts

Hardness

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

Specific Gravity

2.58-2.64 (similar to quartz)

Crystal System

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

Color

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

Luster

Vitreous to waxy

Transparency

Opaque to translucent

Fracture

Conchoidal to splintery

Cleavage

None

Composition

Primarily Silicon Dioxide (SiO2), often with trace impurities of iron, manganese, carbon, copper, chromium, cobalt.

Physical characteristics

• Crystal Habit: Pseudomorph after wood; cryptocrystalline aggregates (chalcedony) or amorphous (opal).
• Cleavage Type: None
• Fracture Type: Conchoidal to splintery
• Tenacity: Brittle
• Luster Type: Vitreous to waxy

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