How to identify Concrete Aggregate

To correctly identify Concrete Aggregate (Artificial aggregate (likely crushed stone or gravel)), 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 grey, black, white, brown, red, or a mix of colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to vitreous, depending on the mineral composition of the source rock.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Rough, angular, sub-angular, sub-rounded, or rounded. Crushed aggregates tend to be angular, while natural gravels are more rounded.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable for aggregate as it is a collection of rock fragments, not a single crystal. Individual mineral grains within the aggregate may exhibit their characteristic crystal forms if visible.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

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

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Aggregates are sourced from quarries (for crushed stone) or natural deposits (for sand and gravel) such as riverbeds, glacial deposits, or ancient marine terraces. The original geological environment of the source rock can be igneous, sedimentary, or metamorphic.

Key Facts

Hardness

Variable, depending on the source rock and its constituent minerals (e.g., quartz 7, calcite 3, feldspar 6-6.5 on Mohs scale).

Specific Gravity

Typically 2.5 to 2.9 for normal-weight aggregates. Lightweight aggregates can be as low as 1.1, and heavy-weight aggregates can exceed 4.0.

Crystal System

Not applicable for aggregate as a whole. Individual mineral grains within the aggregate will have their own crystal systems.

Color

Highly variable, reflecting the source rock.

Luster

Variable, from dull to vitreous.

Transparency

Opaque to translucent, depending on the individual rock fragments and minerals.

Fracture

Conchoidal, uneven, or splintery, depending on the source rock and mineral composition.

Cleavage

Not applicable for aggregate as a whole. Individual mineral grains may exhibit cleavage.

Composition

A mixture of various minerals and rock fragments, commonly including quartz, feldspar, mica, calcite, dolomite, amphibole, pyroxene, and various rock types like granite, basalt, limestone, sandstone, and quartzite.

Physical characteristics

• Crystal Habit: Not applicable for aggregate. Individual mineral grains may show characteristic habits.
• Cleavage Type: Not applicable for aggregate. Individual mineral grains may exhibit perfect, good, or poor cleavage.
• Fracture Type: Variable (conchoidal, uneven, splintery, hackly) depending on the constituent rock and mineral types.
• Tenacity: Brittle (for most common rock types used as aggregate).
• Luster Type: Variable (dull, earthy, vitreous, greasy) depending on the constituent minerals.

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