How to identify Black and Gold Obsidian

To correctly identify Black and Gold Obsidian (Volcanic Glass (SiO2)), 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

   Predominantly black, with a metallic golden sheen or shimmer visible when light reflects off its surface. The sheen can range from subtle to very pronounced.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to sub-vitreous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, conchoidal fracture surfaces. Non-porous.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous; lacks crystal structure.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None. Exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in areas of recent volcanic activity where felsic lava flows have cooled rapidly, typically on the margins of rhyolitic lava flows or domes.

Key Facts

Hardness

5-5.5 on Mohs scale

Specific Gravity

2.35-2.60

Crystal System

Amorphous (lacks crystal structure)

Color

Black with golden sheen

Luster

Vitreous (glassy)

Transparency

Opaque to translucent in thin sections

Fracture

Conchoidal (shell-like, very sharp edges)

Cleavage

None

Composition

Primarily Silicon Dioxide (SiO2), typically 70-75% SiO2, with minor amounts of Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, and H2O.

Physical characteristics

• Crystal Habit: Massive, amorphous
• Cleavage Type: None
• Fracture Type: Conchoidal
• Tenacity: Brittle
• Luster Type: Vitreous (glassy)

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