Snowflake obsidian is a visually unique variety of the naturally occurring volcanic glass known as obsidian. This stone is highly sought after because of its striking contrast between a deep, dark base and scattered light-colored inclusions. The presence of the distinctive white patterns transforms the typically uniform black glass into a speckled stone that draws its name from the appearance of winter precipitation.
Defining the Signature Snowflake Pattern
The most noticeable feature of this stone is the pattern of inclusions that look like tiny, scattered snowflakes across the surface. These markings are typically off-white or gray, providing a stark visual contrast against the stone’s deep, often jet-black background. The individual “snowflakes” are not uniform but appear as small, radially clustered spots and blotches.
The size and density of the light-colored spots vary significantly from one piece to the next, meaning no two samples of snowflake obsidian are exactly alike. In some specimens, the patterns are delicate, creating a subtle speckling effect over the glassy matrix. Other pieces feature larger, more densely packed clusters that can give the stone a heavily mottled or patchy appearance.
These inclusions are scientifically known as spherulites, which are tiny, rounded masses composed of radiating crystals. When polished, the black background retains a smooth, reflective surface. The spherulites can sometimes appear slightly duller or more textural than the surrounding glass.
Essential Physical Characteristics
Snowflake obsidian is primarily composed of silicon dioxide, forming a volcanic glass matrix. The stone shares many characteristics with pure obsidian, including a smooth, glassy texture. Its deep, dark base color is typically black or dark gray, often due to the presence of iron and other transition elements.
Obsidian is an amorphous material, meaning it lacks the repeating atomic structure of a true crystal. This absence of crystalline order is responsible for its characteristic conchoidal fracture, causing the stone to break with smooth, curved surfaces resembling a shell. When polished, the stone exhibits a vitreous luster, giving it a high shine.
On the Mohs scale of mineral hardness, snowflake obsidian ranks between 5 and 6, making it moderately durable. While hard enough for use in jewelry and decorative objects, its inherent glass-like quality means it can be brittle and prone to chipping. The stone is largely opaque, though thin edges may sometimes show slight translucency.
How Snowflake Obsidian Forms
Snowflake obsidian begins its formation through the rapid cooling of high-silica felsic lava from a volcanic eruption. This swift cooling prevents the atoms from arranging into an ordered crystalline structure, resulting in the initial volcanic glass. The distinctive “snowflakes” are the product of a subsequent, slightly slower cooling phase.
This process is a form of partial crystallization, sometimes referred to as devitrification, where the silica molecules begin to rearrange into crystal patterns over time. The white inclusions are composed of the mineral cristobalite, a high-temperature polymorph of quartz. Cristobalite forms needle-shaped crystals that grow outward in a radiating pattern from a central point.
These radiating crystal clusters, known as spherulites, create the visual snowflake effect. This specific partial crystallization occurs because the lava flow cooled slow enough in certain areas, such as underground or in thick, slow-moving flows. This allowed the formation of these microscopic crystals within the glass matrix.