How to identify Sandstone with Lichen

To correctly identify Sandstone with Lichen (Sedimentary rock (likely quartz sandstone) with biological growth), 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

   Sandstone color varies (white, grey, yellow, red, brown, green, black) depending on mineral composition and cement. Lichens add patches or extensive coverings of green, grey, yellow, orange, black, or white.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Sandstone typically has a dull to earthy luster, though quartz grains can exhibit a vitreous luster. Lichens are matte to slightly waxy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Sandstone is clastic, with a gritty feel due to sand grains. Grain size is 0.0625 to 2 mm. Lichens have diverse textures: crustose (crust-like, tightly adhering), foliose (leaf-like, somewhat detached), or fruticose (shrubby, branched).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Sandstone is composed of detrital grains, typically sub-angular to rounded. Lichens do not have a crystal form; they grow in thalli (body structures) characteristic of their species.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Sandstone typically exhibits no cleavage, though it may break along bedding planes. Lichens do not have cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Sandstone forms in various sedimentary environments: fluvial (rivers), eolian (deserts), deltaic, and shallow marine settings. Lichens colonize exposed rock surfaces in almost all terrestrial environments, from polar regions to deserts, requiring only light, air, and moisture. They are common in areas with stable, exposed rock outcrops, cliffs, and boulders.

Key Facts

Hardness

Sandstone: 6-7 (Mohs) for quartz grains; overall rock hardness varies with cementation (can be friable to very hard). Lichens: Not applicable, as they are biological organisms, not minerals.

Specific Gravity

Sandstone: 2.2-2.8 g/cm³ (varies with porosity and mineralogy). Lichens: Not applicable, as they are biological organisms.

Crystal System

Sandstone: Not applicable (composed of detrital grains). Quartz grains are trigonal. Lichens: Not applicable (biological).

Color

Sandstone: White, grey, yellow, red, brown, green, black. Lichens: Green, grey, yellow, orange, black, white.

Luster

Sandstone: Dull to earthy (quartz grains vitreous). Lichens: Matte to slightly waxy.

Transparency

Sandstone: Opaque. Lichens: Opaque.

Fracture

Sandstone: Granular, conchoidal (if well-cemented quartz arenite). Lichens: Not applicable.

Cleavage

Sandstone: None (though may break along bedding planes). Lichens: Not applicable.

Composition

Sandstone: Predominantly quartz (SiO2), with varying amounts of feldspar, rock fragments, and cementing agents (silica, calcite, iron oxides, clay minerals). Lichens: Symbiotic association of a fungus (mycobiont) and an alga or cyanobacterium (photobiont), composed of organic compounds (e.g., carbohydrates, proteins, lipids, lichen acids).

Physical characteristics

• Crystal Habit: Sandstone: Detrital grains, typically rounded to sub-angular. Lichens: Crustose, foliose, or fruticose thalli.
• Cleavage Type: Sandstone: None. Lichens: Not applicable.
• Fracture Type: Sandstone: Granular, conchoidal (for quartz grains). Lichens: Not applicable.
• Tenacity: Sandstone: Brittle. Lichens: Flexible to brittle depending on species and moisture content.
• Luster Type: Sandstone: Earthy to dull (vitreous for quartz). Lichens: Matte.

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