Volcanic glass with winter blooms

Obsidian forms when silica‑rich lava cools so quickly that crystals don’t have time to grow—result: glass. In some flows, residual heat and fluids later coax cristobalite to crystallize in radial, snowflake‑like patches. Hence the name.

Devitrification in action

Those “flakes” are the rock slowly devitrifying—moving from glass toward microcrystalline quartz polymorphs. It’s geology’s way of doodling in the margins.

Spherulite nucleation

Tiny seed points in the glass start to crystallize as cristobalite. Needles radiate outward, creating circular or star‑shaped patches that lighten the black.

Growth & spacing

Flake size and density reflect cooling history: slow, even conditions make larger, well‑spaced “snow”; faster changes make finer, crowded flurries.

Flow memory

Some pieces preserve faint flow banding—subtle grey ribbons within the black glass—with snowflakes perched on top like a winter stream.

Palette

• Ink black — the glass matrix.
• Frost grey to white — cristobalite “flakes.”
• Smoky halos — diffuse rims around larger spherulites.

High polish gives a mirror sheen that makes the flakes appear suspended just beneath the surface.

Pattern words

• Spherulites — round, radial crystal sprays (the “snowflakes”).
• Rosettes — clustered flakes forming larger blossoms.
• Flow bands — subtle ribbons in the glass from viscous movement.
• Hackle marks — tiny feather‑like lines near natural fractures.

Photo tip: Use a large, soft key light to keep the black rich; add a small side light to give each flake a gentle halo without glare.

Spherulite texture

Each flake shows radial fibrous structure (like tiny spokes) and often a slightly darker core where nucleation began.

Glass clues

Edges of chips display shell‑like curves and fine hackle lines—classic glass fracture not seen in crystalline jaspers.

Flow bands

Look for faint, parallel wisps in the black—vestiges of lava movement before the glass froze.

Black jasper with orbs

Jasper is microcrystalline quartz (harder, ~7) and breaks granular, not glassy. Its white spots lack the radial fibrous look of spherulites.

Man‑made glass

Some glasses mimic the look but often show uniform bubbles and lack true spherulite spokes under magnification.

Dalmatian “jasper”

Spots on a beige feldspar‑quartz rock, not black glass; speckles are angular minerals, not radial snowflakes.

Quick checklist

• Mirror‑black, conchoidal chips?
• Round, radial white flakes (not crisp dots)?
• Thin edges glow brown in strong light? → Snowflake obsidian.

Where it shines

Notable sources include Mexico (Sierra de las Navajas), the USA (Oregon’s Glass Buttes, Yellowstone region), parts of Turkey, Armenia, and Iceland. Anywhere rhyolitic volcanism occurs, obsidian may, too—snowflake patterns are a happy after‑story.

How people use it

Polished cabochons, beads, carvings, and smooth palm stones. Historically, obsidian’s razor‑sharp edges made it a go‑to for blades and points (today, it’s mostly for display and jewelry).

Everyday care

• Mild soap + lukewarm water; soft cloth dry.
• Protect from hard knocks—glass is brittle.
• Avoid long ultrasonic/steam cycles and sudden temperature swings.

Jewelry guidance

• Great for pendants, earrings, beads; rings benefit from protective settings.
• Store separately—quartz and corundum can scratch it.
• High polish shows fingerprints; a quick microfiber refresh brings back the mirror.

On the wheel

• Light pressure; obsidian can “orange‑peel” with heat.
• Pre‑polish to 3k–8k diamond; finish with cerium oxide on felt/leather for a piano‑black gloss.
• Chamfer edges slightly to reduce chipping during setting.

Backlight edge

Hold a thin piece to a strong light: the brown edge glow confirms volcanic glass and delights every first‑time viewer.

Snowflake anatomy

With a 10× loupe, trace the radial spokes of a flake from center to rim. That’s cristobalite writing its name in tiny lines.