How to identify Pebble

To correctly identify Pebble (Sedimentary clast), 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 source rock. Can be white, black, grey, brown, red, green, or multicolored.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to vitreous, depending on the mineral composition and surface texture. Often appears dull due to weathering and abrasion.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth and rounded to sub-rounded due to abrasion during transport. The surface may feel gritty if composed of quartz or other hard minerals, or smoother if composed of softer minerals or fine-grained rock.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable, as pebbles are rock fragments, not individual crystals. They exhibit the form of the original rock fragment, modified by transport.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable to the pebble as a whole, but individual mineral grains within the pebble may exhibit cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Fluvial (river beds, floodplains), coastal (beaches, marine terraces), glacial (moraines, outwash plains), alluvial fans, and lacustrine (lake beds) environments.

Key Facts

Hardness

Variable (depends on the constituent minerals and rock type, e.g., quartz pebbles are 7 on Mohs scale, limestone pebbles 3-4)

Specific Gravity

Variable (depends on the constituent minerals and rock type, typically 2.5-3.0 for common rock types)

Crystal System

Not applicable (pebbles are rock fragments)

Color

Highly variable

Luster

Dull to vitreous

Transparency

Opaque to translucent (depending on the rock type)

Fracture

Variable (depends on the rock type, e.g., conchoidal for chert, irregular for granite)

Cleavage

Not applicable to the pebble as a whole

Composition

Variable, composed of fragments of pre-existing igneous, metamorphic, or sedimentary rocks and/or minerals.

Physical characteristics

• Crystal Habit: Not applicable (rock fragment)
• Cleavage Type: Not applicable to the pebble as a whole
• Fracture Type: Variable (depends on the rock type)
• Tenacity: Variable (depends on the rock type)
• Luster Type: Dull, earthy, or vitreous

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