How to identify Concrete

To correctly identify Concrete (Artificial aggregate rock), 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

   Typically grey, but can vary widely depending on the type of cement, aggregates, and any added pigments. White cement produces lighter concrete, while aggregates can impart their natural colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, non-reflective.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Rough and granular due to exposed aggregate particles, or smooth if finished. The internal texture is heterogeneous, showing distinct aggregate clasts embedded in a finer cementitious matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous to microcrystalline cementitious matrix with embedded crystalline and amorphous aggregate particles. No distinct macroscopic crystal forms.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Concrete fractures irregularly.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Not formed in natural geological environments. It is an anthropogenic material, found wherever human construction occurs, from urban centers to remote infrastructure projects.

Key Facts

Hardness

Variable, typically 3-7 on Mohs scale for the cement paste, but aggregate hardness can be higher (e.g., quartz is 7). Overall material hardness is a composite.

Specific Gravity

2.2 - 2.4 g/cm³ for normal weight concrete, but can range from 1.6 to 2.8 g/cm³ depending on aggregate type and porosity.

Crystal System

Not applicable as a whole; the cementitious matrix is largely amorphous to microcrystalline, while aggregates can be crystalline or amorphous.

Color

Grey, white, or colored with pigments; depends on cement and aggregate.

Luster

Dull, earthy.

Transparency

Opaque.

Fracture

Irregular to conchoidal, depending on aggregate and matrix properties.

Cleavage

None.

Composition

Primarily calcium silicate hydrates (CSH), calcium hydroxide (CH), and unreacted cement phases (e.g., tricalcium silicate, dicalcium silicate) forming the matrix, binding various aggregates (e.g., quartz, feldspar, limestone, basalt, granite, shale, sand).

Physical characteristics

• Crystal Habit: Not applicable for the composite material. Cement paste is amorphous to microcrystalline; aggregates retain their original habits.
• Cleavage Type: None.
• Fracture Type: Irregular, conchoidal, or granular, depending on the strength of the aggregate-matrix bond and the fracture characteristics of the aggregate.
• Tenacity: Brittle.
• Luster Type: Dull to earthy.

Explore Concrete