How to identify Sandstone

To correctly identify Sandstone (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

   Highly variable, including white, gray, yellow, tan, brown, red, pink, and green, depending on mineral composition and cementing agent. Iron oxides often impart red, brown, or yellow hues.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to earthy, depending on the cement and porosity. Individual quartz grains may exhibit a vitreous luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Clastic, granular. Grains are sand-sized (0.0625 mm to 2 mm), visible to the naked eye, and feel gritty when rubbed. Can be fine-grained, medium-grained, or coarse-grained. May exhibit bedding planes, cross-bedding, ripple marks, and other sedimentary structures.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual grains are typically detrital, sub-angular to well-rounded, not exhibiting euhedral crystal forms. The rock itself is massive or bedded.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   No rock cleavage. Individual mineral grains (e.g., feldspar) may show cleavage, but the rock as a whole does not cleave along planes. Fracture is more common.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Forms in a wide range of sedimentary environments where sand accumulates, including fluvial (river channels, floodplains), deltaic, beach, shallow marine, eolian (desert dunes), and lacustrine (lake) settings. Often found in thick sequences within sedimentary basins.

Key Facts

Hardness

Variable, typically 6-7 on Mohs scale for quartz grains, but the overall rock hardness depends heavily on the cement. Calcite-cemented sandstone is softer (3), while silica-cemented sandstone (orthoquartzite) can be very hard (7).

Specific Gravity

2.2 - 2.8 g/cm³ (variable, depending on mineral composition and porosity)

Crystal System

Not applicable for the rock as a whole; individual mineral grains (e.g., quartz) are trigonal.

Color

White, gray, yellow, tan, brown, red, pink, green

Luster

Dull to earthy (vitreous for individual quartz grains)

Transparency

Opaque (individual quartz grains can be translucent to transparent)

Fracture

Irregular to conchoidal (for individual quartz grains); granular for the rock as a whole.

Cleavage

None (for the rock); individual mineral grains may exhibit cleavage (e.g., feldspar).

Composition

Predominantly quartz (SiO₂), with varying amounts of feldspar, mica, and rock fragments. Cementing materials include silica (SiO₂), calcite (CaCO₃), iron oxides (e.g., Fe₂O₃), and clay minerals.

Physical characteristics

• Crystal Habit: Clastic, granular; individual grains are detrital and typically sub-angular to well-rounded.
• Cleavage Type: None (as a rock); individual mineral grains may show cleavage.
• Fracture Type: Granular, breaking around the grains; may be conchoidal if silica-cemented and very fine-grained.
• Tenacity: Brittle
• Luster Type: Dull to earthy

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