How to identify Quartz Sandstone

To correctly identify Quartz Sandstone (SiO2 in sedimentary 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

   Highly variable, often light-colored (white, gray, tan, yellow) but can be red, brown, or pink due to iron oxide cements or impurities. Pure quartz sandstone is typically white or light gray.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to vitreous (glassy) on individual quartz grains, overall earthy to gritty.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Clastic, granular, gritty to the touch. Individual sand grains are visible and feel like sand. Grain size ranges from 0.0625 mm to 2 mm. Can be well-sorted (grains of similar size) or poorly sorted.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual quartz grains are typically anhedral (lacking well-formed crystal faces) and can be sub-angular to well-rounded. In some cases, secondary quartz overgrowths can create euhedral crystal faces on the original detrital grains, leading to interlocking textures.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz itself lacks cleavage, exhibiting conchoidal fracture. The sandstone as a whole does not exhibit cleavage, but may break along bedding planes or cementation weaknesses.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in various sedimentary environments where sand accumulates, including fluvial (river), eolian (desert dunes), deltaic, beach, shallow marine, and shelf environments. Requires a source of quartz-rich sediment and conditions for transport, deposition, and subsequent lithification.

Key Facts

Hardness

7 (for individual quartz grains on Mohs scale); overall rock hardness varies with cementation, typically 6-7.

Specific Gravity

2.65 (for quartz); bulk density of sandstone typically 2.2-2.8 g/cm³ depending on porosity and cement.

Crystal System

Trigonal (for quartz mineral)

Color

Variable, often light-colored (white, gray, tan, yellow), but can be red, brown, or pink.

Luster

Dull to gritty (overall), vitreous (individual quartz grains).

Transparency

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

Fracture

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

Cleavage

None (for quartz); the rock does not exhibit cleavage.

Composition

Predominantly silicon dioxide (SiO2) as detrital grains, with minor amounts of other minerals, rock fragments, and cementing agents (e.g., silica, calcite, iron oxides, clay minerals).

Physical characteristics

• Crystal Habit: Anhedral to subhedral grains, often rounded to sub-rounded, sometimes with secondary euhedral overgrowths.
• Cleavage Type: None (quartz is non-cleavable).
• Fracture Type: Conchoidal (for quartz grains); irregular to granular (for the rock as a whole).
• Tenacity: Brittle.
• Luster Type: Vitreous (individual quartz grains); overall dull to gritty.

Explore Quartz Sandstone