How to identify Granite with Lichen

To correctly identify Granite with Lichen (Granite (igneous rock) with biological growth (lichen)), 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

   Granite: Variable, commonly white, gray, pink, or red, with dark specks. Lichen: Highly variable, including white, gray, green, yellow, orange, black, often forming patches or crusts.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Granite: Vitreous to dull (quartz and feldspar), pearly (mica). Lichen: Matte to slightly waxy, depending on species and moisture.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granite: Phaneritic (coarse-grained), equigranular to porphyritic. Lichen: Crustose (crust-like), foliose (leaf-like), or fruticose (shrub-like) growths on the rock surface.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Granite: Anhedral to subhedral interlocking crystals of quartz, feldspar, and mica. Lichen: No crystal form; biological growth with distinct thallus morphology.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Granite: Feldspar exhibits two good cleavages at or near 90 degrees; mica exhibits perfect basal cleavage. Quartz has no cleavage. Lichen: Not applicable (biological).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granite forms in the continental crust at depths of several kilometers, typically associated with orogenic belts and stable cratons. It is exposed at the surface through uplift and erosion. Lichens colonize exposed granite surfaces in diverse environments, from polar regions to deserts, and from sea level to high altitudes, provided there is sufficient light and moisture.

Key Facts

Hardness

Granite: 6-7 on Mohs scale (due to quartz and feldspar). Lichen: Not applicable (biological, soft).

Specific Gravity

Granite: 2.6-2.7 g/cm³. Lichen: Highly variable, typically low due to porous structure.

Crystal System

Granite: Not applicable (polycrystalline aggregate). Individual minerals: Quartz (trigonal), Feldspar (monoclinic/triclinic), Mica (monoclinic). Lichen: Not applicable (biological).

Color

Granite: White, gray, pink, red. Lichen: White, gray, green, yellow, orange, black.

Luster

Granite: Vitreous to dull. Lichen: Matte.

Transparency

Granite: Opaque (individual quartz crystals can be translucent). Lichen: Opaque.

Fracture

Granite: Uneven to conchoidal (quartz). Lichen: Not applicable (biological).

Cleavage

Granite: Good in feldspar and mica, absent in quartz. Lichen: Not applicable (biological).

Composition

Granite: Predominantly quartz (20-60%), alkali feldspar (35-60%), plagioclase feldspar (10-35%), and micas/amphiboles. Lichen: Symbiotic association of a fungus (mycobiont) and a photosynthetic partner (photobiont - alga or cyanobacterium), composed of organic compounds.

Physical characteristics

• Crystal Habit: Granite: Granular, anhedral to subhedral interlocking crystals. Lichen: Crustose, foliose, or fruticose thallus.
• Cleavage Type: Granite: Feldspar (two directions at ~90°), Mica (one perfect basal). Lichen: Not applicable.
• Fracture Type: Granite: Uneven to conchoidal (quartz). Lichen: Not applicable.
• Tenacity: Granite: Brittle. Lichen: Flexible to brittle, depending on species and moisture.
• Luster Type: Granite: Vitreous, dull, pearly. Lichen: Matte.

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