How to identify Granite with Lichen

To correctly identify Granite with Lichen (Granite (Igneous Rock) with Xanthoria parietina (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: Typically pink, white, gray, or black, often speckled. Xanthoria parietina: Bright orange to yellow-orange.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Granite: Vitreous to dull (of individual mineral grains). Lichen: Matte to slightly waxy (of the thallus).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granite: Phaneritic (coarse-grained), interlocking crystalline texture. Lichen: Foliose (leaf-like) or crustose (crust-like) growth on the rock surface, often with distinct lobes.

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 a thallus structure.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Granite: Exhibited by individual mineral components (e.g., feldspar has good cleavage, mica has perfect basal cleavage). Lichen: Not applicable (biological organism).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granite: Intrusive igneous bodies (batholiths, stocks, dikes) formed in continental crust, often associated with orogenic belts. Lichen: Exposed rock surfaces in a wide range of climates, from coastal to alpine, particularly in areas with moderate air quality and sunlight.

Key Facts

Hardness

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

Specific Gravity

Granite: 2.65-2.75 g/cm³. Lichen: Varies, very low density when dry.

Crystal System

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

Color

Granite: Variable (pink, gray, white, black). Lichen: Bright orange to yellow-orange.

Luster

Granite: Vitreous to dull. Lichen: Matte.

Transparency

Granite: Opaque. Lichen: Opaque.

Fracture

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

Cleavage

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

Composition

Granite: Primarily quartz (20-60%), alkali feldspar (35-60%), plagioclase feldspar (10-35%), mica (biotite, muscovite), amphibole. Lichen (Xanthoria parietina): Symbiotic association of a fungus (mycobiont, typically an ascomycete) and a green alga (photobiont, Trebouxia).

Physical characteristics

• Crystal Habit: Granite: Granitic (equigranular, interlocking crystals). Lichen: Foliose (leaf-like) thallus.
• Cleavage Type: Granite: Good in feldspar (two directions at ~90°), perfect basal in mica. Lichen: Not applicable.
• Fracture Type: Granite: Uneven to conchoidal (quartz). Lichen: Not applicable.
• Tenacity: Granite: Brittle. Lichen: Flexible when wet, brittle when dry.
• Luster Type: Granite: Vitreous to dull. Lichen: Matte.

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