How to identify Quartz Sandstone

To correctly identify Quartz Sandstone (Quartz sandstone), 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 light-colored: white, gray, tan, yellow, brown, or reddish. Color variations are often due to minor impurities or cementing agents (e.g., iron oxides for red/brown hues).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to vitreous (glassy) on freshly broken surfaces, depending on the degree of cementation and the luster of individual quartz grains.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Clastic, granular, with sand-sized grains (0.0625 mm to 2 mm). Grains are often well-sorted and well-rounded in mature quartz sandstones. Can feel gritty to the touch.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual quartz grains are typically anhedral to subhedral, often rounded due to transport. In highly cemented varieties, quartz overgrowths can create euhedral crystal faces within the pore spaces.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No rock cleavage. Individual quartz grains exhibit poor to indistinct cleavage (rhombohedral), but this is rarely observed in hand samples of sandstone.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in high-energy sedimentary environments where clastic sediments are transported and deposited, such as beaches, dunes (deserts), river channels, deltas, and shallow marine shelves. These environments promote the removal of unstable minerals and fine-grained matrix, leading to a high concentration of resistant quartz grains.

Key Facts

Hardness

Individual quartz grains are 7 on Mohs scale; the rock's overall hardness depends on cementation, typically 6-7 for well-cemented varieties.

Specific Gravity

2.65 - 2.70 (for pure quartz grains; the rock's bulk specific gravity can vary with porosity and cement type, typically 2.2 - 2.6).

Crystal System

Trigonal (for individual quartz grains). The rock itself is an aggregate of grains.

Color

White, gray, tan, yellow, brown, reddish.

Luster

Dull to vitreous.

Transparency

Opaque to translucent (for the rock; individual quartz grains can be transparent).

Fracture

Conchoidal (for individual quartz grains); irregular to granular for the rock.

Cleavage

None (for the rock); individual quartz grains have poor/indistinct rhombohedral cleavage.

Composition

Predominantly quartz (SiO2), typically >90%. Minor constituents may include feldspar, mica, heavy minerals, and various cementing agents (silica, calcite, iron oxides, clay minerals).

Physical characteristics

• Crystal Habit: Anhedral to subhedral, often rounded grains of quartz.
• Cleavage Type: Not applicable for the rock; individual quartz grains exhibit poor/indistinct rhombohedral cleavage.
• Fracture Type: Irregular to granular for the rock; conchoidal for individual quartz grains.
• Tenacity: Brittle.
• Luster Type: Dull to vitreous.

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