How to identify Unidentified Rock

To correctly identify Unidentified Rock (Unknown), 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; can be any color or combination of colors.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Highly variable; can be metallic, submetallic, vitreous, dull, earthy, greasy, waxy, pearly, silky, or resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Highly variable; can be fine-grained, coarse-grained, porphyritic, vesicular, foliated, non-foliated, clastic, crystalline, etc.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Highly variable; may show distinct crystal forms if it's a mineral, or be an aggregate of crystals or grains if it's a rock.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Highly variable; presence or absence of cleavage, and the number and angles of cleavage planes, depend on the constituent minerals.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Unknown; could originate from any geological setting (e.g., volcanic, plutonic, sedimentary basin, metamorphic belt).

Key Facts

Hardness

Variable (1-10 on Mohs scale)

Specific Gravity

Variable (typically 1.0 - 20.0 g/cm³)

Crystal System

Variable (if crystalline, can be any of the 7 crystal systems)

Color

Variable

Luster

Variable

Transparency

Variable (opaque, translucent, transparent)

Fracture

Variable (conchoidal, uneven, hackly, splintery, earthy)

Cleavage

Variable (present or absent, 1 to 6 directions)

Composition

Unknown; requires chemical analysis to determine.

Physical characteristics

• Crystal Habit: Variable (e.g., massive, granular, bladed, prismatic, tabular, acicular)
• Cleavage Type: Variable (e.g., perfect, good, poor, none)
• Fracture Type: Variable (e.g., conchoidal, uneven, hackly, splintery, earthy)
• Tenacity: Variable (e.g., brittle, malleable, ductile, sectile, flexible, elastic)
• Luster Type: Variable (e.g., metallic, submetallic, vitreous, dull, earthy, greasy, waxy, pearly, silky, resinous)

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