How to identify Snowflake Obsidian

To correctly identify Snowflake Obsidian (Volcanic Glass (Obsidian) with Spherulites), 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

   Black to dark gray with white to light gray 'snowflake' patterns (spherulites).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, conchoidal fracture, amorphous matrix with visible crystalline spherulites.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Amorphous (glassy) matrix with radial, spherical aggregates of microcrystalline minerals (spherulites).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   None (due to its amorphous nature).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Volcanic regions where felsic lava cools rapidly, typically in lava flows, domes, or margins of dikes and sills.

Key Facts

Hardness

5 to 5.5 on the Mohs scale (due to its glassy nature, it is relatively brittle)

Specific Gravity

2.35 to 2.60 g/cm³

Crystal System

Amorphous (lacks a crystalline structure in its bulk, though spherulites are microcrystalline)

Color

Black to dark gray with white to light gray spherulites

Luster

Vitreous (glassy)

Transparency

Opaque to translucent on thin edges

Fracture

Conchoidal (sharp, curved, shell-like fractures)

Cleavage

None

Composition

Primarily silicon dioxide (SiO₂) with minor amounts of aluminum, sodium, potassium, iron, and other elements. The spherulites are typically cristobalite (a high-temperature polymorph of SiO₂) or feldspar minerals.

Physical characteristics

• Crystal Habit: Amorphous mass with embedded radial spherulites.
• Cleavage Type: Absent.
• Fracture Type: Conchoidal, producing extremely sharp edges.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy).

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