How to identify Gravel

To correctly identify Gravel (Mixed Sedimentary 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, depending on the source rocks. Can be white, grey, black, brown, red, yellow, or a mix of these colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to vitreous, depending on the constituent minerals and rock fragments. Often appears earthy or dull due to surface weathering and dust.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Coarse-grained, gritty, and rough to the touch. Individual particles are discernible by eye and touch. Particle shapes range from angular to well-rounded.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable, as gravel consists of rock fragments, not individual crystals with defined external forms. Individual mineral grains within the fragments may exhibit crystal forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable to the aggregate as a whole. Individual mineral grains within the rock fragments may exhibit cleavage (e.g., feldspar, mica).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Fluvial (riverbeds, floodplains, terraces), glacial (moraines, outwash plains), marine (beaches, nearshore environments), lacustrine (lake shores), alluvial fans, colluvial deposits (talus slopes).

Key Facts

Hardness

Variable (depends on constituent minerals, typically 3-7 on Mohs scale for individual grains)

Specific Gravity

Variable (typically 2.5-2.8 for common rock-forming minerals)

Crystal System

Not applicable (aggregate of rock fragments)

Color

Highly variable (white, grey, black, brown, red, yellow, mixed)

Luster

Dull, earthy, or vitreous (depending on components)

Transparency

Opaque to translucent (for individual fragments)

Fracture

Conchoidal, irregular, or splintery (depending on constituent rock types)

Cleavage

Not applicable to the aggregate; present in some constituent minerals

Composition

Mixed mineral grains and rock fragments (e.g., quartz, feldspar, granite, basalt, limestone, sandstone, shale)

Physical characteristics

• Crystal Habit: Not applicable (aggregate of fragments)
• Cleavage Type: Not applicable to the aggregate; varies for constituent minerals
• Fracture Type: Variable (depends on constituent rock types)
• Tenacity: Brittle (individual fragments)
• Luster Type: Variable (dull, earthy, vitreous)

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