How to identify Gravel

To correctly identify Gravel (Unconsolidated sediment composed of rock fragments), 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, depends on the source rock fragments. Can be grey, brown, white, black, red, or a mix of colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Variable, depends on the individual mineral grains and rock fragments. Can be dull, earthy, vitreous, or glassy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Clastic, granular, unconsolidated. Individual grains are typically visible and feel gritty. Grain size ranges from 2 mm to 64 mm.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable for gravel as a whole; individual mineral grains within the gravel may exhibit crystal forms, but the rock fragments are typically anhedral to subhedral.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable for gravel as a whole; individual mineral grains within the gravel may exhibit cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Fluvial (riverbeds, floodplains, terraces), glacial (moraines, outwash plains), marine (beaches, offshore bars), lacustrine (lake shores), colluvial (talus slopes).

Key Facts

Hardness

Variable (depends on constituent minerals/rocks, e.g., quartz is 7 on Mohs scale)

Specific Gravity

Variable (typically 2.5-2.8 for common rock types like granite, basalt, limestone)

Crystal System

Not applicable (unconsolidated aggregate)

Color

Highly variable, reflecting source rocks

Luster

Variable, reflecting constituent minerals

Transparency

Opaque to translucent (for individual fragments)

Fracture

Variable (conchoidal, irregular, splintery, depending on constituent minerals/rocks)

Cleavage

Not applicable (unconsolidated aggregate)

Composition

Heterogeneous, composed of fragments of various rocks (igneous, metamorphic, sedimentary) and minerals (e.g., quartz, feldspar, mica, calcite).

Physical characteristics

• Crystal Habit: Not applicable (aggregate of fragments)
• Cleavage Type: Not applicable (aggregate of fragments)
• Fracture Type: Variable, depending on constituent rock/mineral fragments
• Tenacity: Brittle (for individual fragments)
• Luster Type: Variable (e.g., dull, earthy, vitreous)

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