Obsidian is a natural volcanic glass, distinct from traditional rocks because its structure is amorphous, meaning it lacks the organized crystal lattice found in minerals. It forms from the rapid cooling of specific types of lava, resulting in a dark, glassy material. Snowflake obsidian is a visually striking variety of this volcanic glass, characterized by its black base color speckled with white, blotchy patterns that resemble snowflakes.
The Geological Origins of Obsidian
Obsidian formation begins deep within the Earth’s crust with felsic magma, which is highly saturated with silicon dioxide, typically exceeding 70% silica content. This high concentration of silica results in lava with extremely high viscosity, meaning it is thick and resistant to flow. When this viscous, silica-rich lava is extruded onto the Earth’s surface during a volcanic eruption, it cools with remarkable speed.
The rapid cooling process is the primary factor in the formation of obsidian. Under normal cooling conditions, atoms in molten rock have enough time to organize themselves into repeating mineral crystal structures. However, the quick drop in temperature inhibits the diffusion of these atoms, freezing the material into a solid state before crystallization can occur.
The resulting material is volcanic glass—a non-crystalline, or amorphous, solid. This base material is typically a uniform jet-black color due to minute inclusions of iron oxides like magnetite. This glassy composition is why obsidian fractures with a characteristic conchoidal pattern.
The Mineralogical Explanation for the “Snowflakes”
The distinctive white patterns in snowflake obsidian represent a modification of the base volcanic glass through devitrification. Devitrification is the geological process where an amorphous glass structure slowly begins to revert to a crystalline state over time. This change is often triggered by minor temperature fluctuations or the presence of water vapor after the initial rapid cooling.
The “snowflakes” are clusters of tiny, radiating crystals called spherulites. These spherulites form when the silica atoms within the glass start to nucleate around a central point, growing outward in a spherical aggregate. The mineral component that makes up these white spherulites is primarily cristobalite, which is a polymorph of silica.
Cristobalite has the same chemical formula as quartz, silicon dioxide, but possesses a different crystal structure that is stable at very high temperatures. The devitrification process allows this high-temperature polymorph to form in a metastable state within the cooling volcanic glass. The contrast between the black, non-crystalline obsidian and the white, radially clustered cristobalite spherulites creates the unique, mottled pattern.
Abundance and Commercial Rarity Assessment
Geologically, snowflake obsidian is not considered a rare material, and commercially, it is widely available. It is one of the more common types of patterned obsidian found in the global gemstone market. Its widespread availability is due to the frequency with which the devitrification process occurs in older obsidian flows.
Snowflake obsidian is sourced from numerous locations worldwide that have experienced rhyolitic volcanism. Significant deposits are found in the Western United States, including areas in Oregon, Arizona, and Utah. Mexico is also a major source, contributing to the steady supply that meets commercial demand.
When assessing its scarcity, it is helpful to compare snowflake obsidian to truly uncommon varieties. For instance, the iridescent sheen of rainbow obsidian, which is caused by the precise alignment of internal gas bubbles and minute mineral crystals, is considerably less common in the trade. Similarly, certain rare mahogany patterns or clear, high-quality gold sheen obsidians can command higher prices and are scarcer than the readily available snowflake variety.
The unique and appealing appearance of snowflake obsidian has made it a popular material for jewelry and decorative objects. Its beauty does not correlate with market scarcity, as the geological conditions required for its formation are frequent enough to sustain a large-scale supply.