How to identify Weathered Rock with Lichen

To correctly identify Weathered Rock with Lichen (Indeterminate rock type with biological growth (lichen/moss)), 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, depending on the underlying rock type and the species of lichen/moss. Rock colors can range from black, grey, white, red, brown, green, or yellow. Lichens can be grey, green, yellow, orange, red, black, or white. Mosses are typically various shades of green, yellow-green, or brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   The rock surface may exhibit a dull, earthy, or weathered luster. The lichen/moss growth typically has a matte or dull appearance, though some lichens can appear slightly waxy or powdery.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   The rock texture will be characteristic of its type, but weathering may make it rough, pitted, granular, or friable. The lichen growth can be crustose (crust-like, tightly adhering), foliose (leaf-like, somewhat detached), or fruticose (shrubby, branched). Mosses form soft, velvety, or spongy mats.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Not applicable to the overall 'Weathered Rock with Lichen' as it's a composite. The underlying rock may or may not exhibit crystal forms depending on its lithology (e.g., euhedral crystals in igneous rocks, clastic grains in sedimentary rocks).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Not applicable to the overall 'Weathered Rock with Lichen'. The underlying rock may exhibit cleavage planes depending on its mineralogy and metamorphic history.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in virtually all terrestrial environments where rocks are exposed to the atmosphere and light, from polar regions to deserts, high mountains to coastal areas. Requires sufficient moisture (even if intermittent) for biological growth. Common on outcrops, boulders, cliffs, gravestones, and man-made structures.

Key Facts

Hardness

Variable (depends on the underlying rock, lichens/mosses are soft)

Specific Gravity

Variable (depends on the underlying rock, lichens/mosses are low density)

Crystal System

Not applicable (composite material)

Color

Highly variable, combination of rock and biological growth colors

Luster

Dull, earthy, or matte

Transparency

Opaque (rock) / Opaque to translucent (lichen/moss)

Fracture

Variable (depends on the underlying rock)

Cleavage

Variable (depends on the underlying rock)

Composition

Silicate, carbonate, or other rock-forming minerals (for the rock) + organic compounds (for lichen/moss)

Physical characteristics

• Crystal Habit: Not applicable (composite material)
• Cleavage Type: Variable (depends on the underlying rock)
• Fracture Type: Variable (depends on the underlying rock)
• Tenacity: Variable (depends on the underlying rock; lichens/mosses are brittle or flexible)
• Luster Type: Dull, earthy, matte

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