Snowflake Obsidian: Physical & Optical Characteristics
Linas JuozenasShare
Physical and optical characteristics
Snowflake Obsidian: Glass, Spherulites, and Frosted Contrast
Snowflake obsidian is natural volcanic glass patterned by pale internal spherulites. The dark host formed when silica-rich lava cooled quickly into glass; the snowflake-like markings developed later as portions of the glass devitrified into microcrystalline, commonly cristobalite-rich, radial clusters.
- Material: volcanic glass
- Pattern: pale cristobalite-rich spherulites
- Hardness: about Mohs 5–5.5
- Optical character: isotropic glass
- Typical RI: about 1.49–1.51
Material Identity
Snowflake obsidian is a patterned variety of obsidian, the natural glass produced when high-silica volcanic melt cools too quickly for atoms to arrange into a fully crystalline rock. The base is amorphous volcanic glass, while the pale inclusions are internal spherulites formed by devitrification.
The name is descriptive. “Snowflake” refers to the pale, radial clusters that resemble frost, flowers, stars, or flakes scattered across black glass. These markings are not paint, dye, surface crust, trapped snow, or fossil material. They are mineral growths inside the glass, commonly described as cristobalite-rich spherulites.
Physical and Optical Properties at a Glance
The values below are typical for snowflake obsidian and may vary slightly by lava flow, alteration, thickness, and testing method.
| Property | Typical snowflake obsidian | Interpretive note |
|---|---|---|
| Material type | Natural volcanic glass; mineraloid rather than a single crystal mineral. | The base lacks long-range crystal structure, unlike quartz, jasper, or feldspar. |
| Common composition | Silica-rich rhyolitic glass, commonly about 70% or more SiO2, with aluminum, sodium, potassium, iron, and trace constituents. | Exact chemistry varies by volcanic source and cooling history. |
| Pattern material | Pale radial spherulites, commonly cristobalite-rich microcrystalline aggregates. | These are natural internal devitrification features, not a surface coating. |
| Crystal system | None for the glass host; amorphous. | The snowflake clusters themselves are microcrystalline. |
| Color | Black, charcoal, smoky gray, or gray-black with white to pale gray flakes. | Thin edges may transmit brownish or smoky light. |
| Luster | Vitreous on polished or fresh glass; softer and satiny over spherulitic areas. | Strong polish can make the dark base highly reflective. |
| Transparency | Usually opaque in hand specimens; translucent on thin edges or chips. | Edge lighting can help distinguish glass from denser, waxier look-alikes. |
| Hardness | About Mohs 5–5.5. | Softer than quartz and many jaspers; polished surfaces can scuff if stored carelessly. |
| Specific gravity | About 2.35, with natural variation. | Often feels lighter than jasper or agate of comparable size. |
| Cleavage | None. | It breaks like glass, not along mineral cleavage planes. |
| Fracture and tenacity | Conchoidal fracture; brittle. | Broken edges can be sharp and should be handled carefully. |
| Refractive index | Single reading commonly around 1.49–1.51. | The glass base is isotropic and does not show true birefringence. |
| Optical character | Isotropic for the glass host. | Weak anomalous effects may appear from strain, inclusions, or microcrystalline zones. |
| Pleochroism | None in the glass host. | Isotropic materials do not display pleochroism. |
| Fluorescence | Usually inert or not diagnostic. | Ultraviolet response is not a reliable identification feature. |
| Chemical sensitivity | Insoluble in water; avoid harsh chemicals, abrasives, and strong etchants. | Routine cleaning should be gentle to preserve polish. |
Optical Behavior: Why the Flakes Look Frosted
The dark host and pale inclusions behave differently with light. The host behaves like glass; the spherulites behave like dense, light-scattering microcrystalline clusters.
Isotropic glass host
Because the host is glass, light normally travels through it without the directional splitting seen in birefringent crystals. In gemological terms, the base has a single refractive index and is optically isotropic.
Frosted spherulites
The pale clusters scatter light through countless tiny boundaries, fibers, and interfaces. This scattering makes the spherulites appear soft white or pale gray even though they are enclosed in dark glass.
Color, Contrast, and Stability
The classic appearance is a strong black-and-white contrast, but natural examples range from high-contrast black glass with crisp white blooms to softer charcoal material with gray or cream-toned flakes.
Dark base color
The black to smoky-gray body color comes from the glass composition, trace elements, microscopic inclusions, oxidation state, and the thickness of the piece. Thin edges may transmit warm brown or smoky light.
Pale snowflakes
The white or gray snowflake effect is caused by light scattering from microcrystalline spherulites. A flake may appear soft and diffuse or sharply radial depending on growth texture and polish.
Pattern density
Spherulites may be sparse, evenly scattered, clustered, flow-aligned, or merged into lacy fields. Density reflects nucleation sites, chemistry, water content, and local devitrification history.
Light stability
The color and pattern are generally stable in normal indoor display and ordinary indirect daylight. The larger risks are impact, abrasion, and sudden temperature change rather than fading.
Textures and Fabric
Snowflake obsidian is a textural stone. Its most important visible features are the glassy host, pale spherulites, possible flow bands, perlitic cracks, and conchoidal fracture surfaces.
| Feature | What it looks like | What it means |
|---|---|---|
| Spherulites | Round, floral, star-like, or soft-edged white to gray patches. | Radial microcrystalline growths formed as glass devitrified. |
| Flow bands | Curved, smoky, or ribbon-like lines through the dark glass. | They record movement and shearing of viscous lava before the glass fully solidified. |
| Perlitic cracks | Curved, onion-skin, circular, or shell-like crack networks. | Hydration and contraction in volcanic glass can create these arcs; they may be stable but should be disclosed in specimens and jewelry. |
| Conchoidal fracture | Smooth curved break surfaces, sometimes with very sharp edges. | Classic glass fracture; useful for identification and important for safe handling. |
| Mirror polish | High reflected highlights on the dark host, interrupted by frosted pale areas. | Fine polish increases contrast but also reveals scratches, dust, and flat spots quickly. |
| Edge translucence | Thin edges glow smoky brown or gray under strong light. | Typical of obsidian and useful in separating it from opaque crystalline rocks. |
Identification and Look-Alikes
Snowflake obsidian is identified by its glassy base, conchoidal fracture, moderate hardness, lower density than jasper, and natural internal spherulites. Pattern alone is not enough, because several stones and artificial glasses can appear spotted or black-and-white.
Useful non-destructive checks
- Look for vitreous luster and mirror-like reflection on polished areas.
- Inspect edges for conchoidal fracture and smoky translucence.
- Use a loupe to check whether pale flakes are internal and radially textured.
- Compare heft: obsidian is often lighter than jasper or agate of the same size.
- Use refractive index testing when an appropriate polished surface allows it.
Common look-alikes
- Snowflake jasper: denser, harder, waxier, and microgranular rather than glassy.
- Dalmatian stone: pale rock with black spots, not dark glass with pale spherulites.
- Gabbro or diorite: crystalline igneous rocks with visible mineral grains.
- Artificial glass: may show repeated bubbles, surface-applied pattern, or unnaturally uniform dots.
- Painted or composite material: pattern may sit at the surface rather than inside the glass.
Viewing and Photographing Snowflake Obsidian
Polished black glass is visually striking but demanding to photograph. Controlled light helps reveal the snowflakes without turning the surface into glare.
Use soft side light
A diffused light at a low to moderate angle can make the dark base read as glossy while giving the pale spherulites enough contrast to stand out.
Avoid extreme backgrounds
Pure black can hide the edge of the stone, while pure white can wash out pale flakes. Neutral gray, muted slate, or softly graduated backgrounds are often more effective.
Control reflections
A polarizing filter may reduce hot spots. Keep the camera, hands, and bright objects out of the reflection zone when photographing mirror-polished pieces.
Clean gently first
Dust, lint, and fingerprints show quickly on polished obsidian. Use a clean microfiber cloth and avoid rough wiping that could scuff the surface.
Care, Handling, and Storage
Snowflake obsidian should be cared for as glass: beautiful, polishable, and useful in jewelry, but not immune to chips, scratches, or thermal stress.
Cleaning
Use a soft dry or lightly damp cloth. Mild soap and brief lukewarm water contact are usually sufficient when needed; dry promptly. Avoid abrasive powders, strong solvents, acids, steam, and ultrasonic cleaning.
Temperature
Avoid sudden temperature changes, open flame, hot windowsills, and intense display lamps. Thermal shock can stress glass and may worsen existing hairlines or chips.
Storage
Store separately from harder stones, metal edges, keys, and abrasive grit. A lined box, soft pouch, or divided tray protects the polish and edges.
Jewelry use
Pendants, earrings, beads, and protected cabochons are generally safer than exposed rings. Thin points, drilled holes, and sharp edges should be inspected before wear.
Questions Readers Often Ask
Are the white snowflakes natural?
Yes. In natural snowflake obsidian, the pale markings are internal spherulites formed as volcanic glass devitrified. They are not paint, dye, surface crust, or trapped snow.
Can the snowflakes rub off?
No. The spherulites are internal features of the glass. However, the polished surface above them can scratch or dull if it is abraded.
How is snowflake obsidian different from plain black obsidian?
Both are volcanic glass. Plain black obsidian lacks the pale devitrification spherulites that create the snowflake pattern.
Why do the edges sometimes look brownish?
Thin obsidian edges can transmit smoky brown or gray light. This is normal for many dark volcanic glasses and can help distinguish glass from fully opaque crystalline rocks.
Is snowflake obsidian rare?
It is not usually rare, but high-contrast material with crisp, well-spaced, attractive spherulites and excellent polish is more selective than ordinary patterned rough.
Can snowflake obsidian go in water?
Brief contact with plain water is generally acceptable for cleaning, followed by prompt drying. Long soaking, hot water, chemicals, salt baths, and abrasive cleaning are unnecessary and should be avoided.
The Takeaway
Snowflake obsidian is the physical record of rapid cooling followed by slow internal change. Silica-rich lava quenched into dark volcanic glass; later devitrification produced pale cristobalite-rich spherulites that scatter light like frost within the black host. Its key identifying traits are a glassy luster, conchoidal fracture, Mohs hardness near 5–5.5, specific gravity around 2.35, a single refractive index near 1.49–1.51, and internal snowflake-like spherulites. Treat it as polished glass: protect the edges, avoid abrasion and thermal shock, and let careful lighting reveal the quiet contrast that makes the stone so recognizable.