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Snowflake Obsidian is a naturally occurring volcanic glass characterized by its opaque black or dark gray groundmass punctuated by distinctive white to grayish-white, radially crystallized inclusions that resemble snowflakes. These inclusions are composed of cristobalite, a high-temperature silica mineral. The contrast between the dark, glassy obsidian and the lighter, crystalline spherulites gives this rock its unique and appealing appearance. It exhibits a conchoidal fracture, typical of obsidian, and a vitreous luster.
How to Identify
- Color
- Black to dark gray groundmass with white to grayish-white 'snowflake' patterns.
- Luster
- Vitreous (glassy) on fresh surfaces.
- Texture
- Smooth, glassy groundmass with slightly rougher, crystalline inclusions.
- Crystal Form
- Amorphous (glassy) matrix with spherulitic (radial fibrous) inclusions of cristobalite.
- Cleavage
- None; exhibits conchoidal fracture.
- Geological Environment
- Found in areas of recent or geologically young felsic volcanic activity, typically associated with rhyolitic lava flows and domes.
Key Facts
- Hardness: 5-5.5 on the Mohs scale (for the glassy matrix)
- Specific Gravity: 2.35-2.60
- Crystal System: Amorphous (glassy) matrix; Cristobalite inclusions are tetragonal (high-temperature form) or orthorhombic (low-temperature form)
- Color: Black to dark gray with white to grayish-white inclusions
- Luster: Vitreous (glassy)
- Transparency: Opaque
- Fracture: Conchoidal
- Cleavage: None
- Composition: Primarily SiO2 (silica) with minor amounts of Al2O3, Fe2O3, MgO, CaO, Na2O, K2O, and H2O. The white inclusions are composed of cristobalite (SiO2).
Quick Check
- Color: Black with white 'snowflakes'
- Luster: Vitreous (glassy)
- Streak: White (due to its amorphous nature and high silica content, it does not produce a colored streak)
Physical Characteristics
- Crystal Habit: Amorphous (glassy) for the matrix; spherulitic (radial fibrous aggregates) for the cristobalite inclusions.
- Cleavage Type: None
- Fracture Type: Conchoidal, producing very sharp edges.
- Tenacity: Brittle
- Luster Type: Vitreous (glassy)
Formation
Snowflake Obsidian forms from the rapid cooling of felsic lava (rich in silica), preventing the formation of large crystals and resulting in a glassy texture. The distinctive 'snowflake' patterns are spherulitic inclusions of cristobalite, a high-temperature polymorph of silica. These spherulites crystallize from the glass during devitrification, a process where the amorphous glass begins to crystallize, often initiated by the presence of water or other volatiles, or by slow cooling after initial rapid quenching. The cristobalite forms radially outward from a central nucleation point, creating the characteristic white, star-like or snowflake-like patterns within the black obsidian matrix.
Usage
Primarily used as an ornamental stone, for carving, cabochons, beads, and decorative objects. Historically, like other obsidians, it may have been used for tools and weapons by indigenous cultures, though its aesthetic qualities make it more valued for decorative purposes today. It is also popular in metaphysical and spiritual practices.
Age Distribution
Typically Cenozoic to recent, associated with active volcanism.
Where to Find
United States
Oregon, Utah, Arizona, California, and Nevada are significant sources, particularly in areas with extensive rhyolitic volcanism.
Mexico
Various volcanic regions in Mexico yield Snowflake Obsidian.
Iceland
Known for its diverse volcanic rocks, including obsidian varieties.
Italy
Lipari Island is a historical source of obsidian, including some with spherulitic textures.
Greece
Milos Island is another historical source of obsidian.
Finding Tips
Volcanic Regions
Focus your search in areas known for recent or geologically young felsic volcanic activity, particularly where rhyolitic lava flows have occurred.
Outcrops and Talus Slopes
Look for obsidian in outcrops, eroded stream beds, and talus slopes below volcanic cliffs. Obsidian is often found as nodules, blocks, or flow bands.
Conchoidal Fracture
Identify obsidian by its characteristic conchoidal (shell-like) fracture. Freshly broken surfaces will be sharp and glassy.
Associated Minerals
Snowflake obsidian is often found alongside other volcanic rocks and minerals such as pumice, perlite, and various forms of quartz.
Safety Precautions
Obsidian edges are extremely sharp. Handle with care and wear appropriate gloves to prevent cuts. Always be aware of your surroundings in volcanic terrains, which can be unstable.
Similar Rocks
Obsidian
Obsidian
Also known as: Volcanic Glass
Apache Tears
Obsidian nodules
Also known as: Marekanite
Perlite
Hydrated Obsidian
Also known as: Volcanic Glass
Scientific Classification
- Mineral Class
- Volcanic Glass (not a true mineral due to its amorphous structure, but composed primarily of silica)
- Group
- Silicates (specifically, a natural glass)
- Crystal System
- Amorphous (for obsidian); Tetragonal or Orthorhombic (for cristobalite inclusions)
- Chemical Formula
- SiO2 (amorphous) with minor impurities; Cristobalite is SiO2
- Composition
- Predominantly silicon dioxide (SiO2), typically 70-75% by weight, with varying amounts of other oxides.
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