How to identify Quartz-Aggregate Concrete

To correctly identify Quartz-Aggregate Concrete (Artificial aggregate with SiO2), 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 cement color (typically grey) and the color of the quartz aggregate (white, clear, pink, brown, black, etc.). Can also be pigmented.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy for the cement matrix; vitreous to greasy for exposed quartz aggregate surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Rough to smooth, depending on the aggregate size, finishing techniques, and exposure of aggregates. Typically granular due to the presence of aggregates.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   No inherent crystal form for the composite material. Individual quartz grains within the concrete will exhibit their characteristic anhedral to subhedral forms, often fractured.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No cleavage for the composite material. Individual quartz grains lack cleavage but exhibit conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Not a naturally occurring rock. Found in anthropogenic environments globally, wherever construction occurs. It is a manufactured material, not formed by geological processes.

Key Facts

Hardness

Variable; cement paste typically 3-5 (Mohs), quartz aggregate 7 (Mohs). Overall composite hardness is not a single value.

Specific Gravity

Typically 2.2 - 2.4 for normal weight concrete, but can vary based on aggregate density (quartz is ~2.65).

Crystal System

Amorphous (cement paste) with embedded trigonal (quartz) crystals.

Color

Grey, white, or colored, with embedded clear, white, or colored quartz grains.

Luster

Dull to earthy (cement matrix), vitreous to greasy (quartz aggregate).

Transparency

Opaque (cement matrix), translucent to transparent (quartz aggregate).

Fracture

Irregular to conchoidal (composite), conchoidal (quartz aggregate).

Cleavage

None (composite), none (quartz aggregate).

Composition

Hydrated calcium silicates, calcium aluminates, calcium aluminoferrites (from cement hydration), and silicon dioxide (SiO2) as quartz aggregate, along with minor impurities.

Physical characteristics

• Crystal Habit: Not applicable for the composite. Quartz aggregates are typically anhedral to subhedral grains.
• Cleavage Type: None.
• Fracture Type: Irregular to conchoidal for the composite; conchoidal for individual quartz grains.
• Tenacity: Brittle.
• Luster Type: Dull to earthy for the cement matrix; vitreous to greasy for exposed quartz aggregate.

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