How to identify Green Obsidian

To correctly identify Green Obsidian (Volcanic Glass (Obsidian)), 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

   Ranges from dark green, olive green, to sometimes a translucent emerald green. The color is often uniform but can show subtle banding.

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, homogeneous, and glassy. May contain microscopic bubbles or flow bands.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous; lacks crystal structure. It is a natural glass.

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 or geologically young silicic volcanic activity, typically associated with rhyolitic lava flows, domes, or volcanic necks. It forms where lava cools very rapidly, preventing crystal growth.

Key Facts

Hardness

5 to 5.5 on the Mohs scale.

Specific Gravity

2.35 to 2.60 g/cm³.

Crystal System

Amorphous (non-crystalline).

Color

Dark green, olive green, emerald green.

Luster

Vitreous (glassy).

Transparency

Translucent to opaque, sometimes transparent in thin sections.

Fracture

Conchoidal (shell-like, producing very sharp edges).

Cleavage

None.

Composition

Primarily silicon dioxide (SiO2), typically 70-75% by weight, with minor amounts of aluminum oxide (Al2O3), sodium oxide (Na2O), potassium oxide (K2O), iron oxides (FeO, Fe2O3), and magnesium oxide (MgO). The green color is often due to trace ferrous iron (Fe2+) or microscopic mineral inclusions.

Physical characteristics

• Crystal Habit: Massive, amorphous.
• Cleavage Type: None.
• Fracture Type: Conchoidal, producing extremely sharp edges.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy).

Explore Green Obsidian