Obsidian is a natural volcanic glass formed when lava cools so rapidly that mineral crystals do not have time to grow. This process creates a smooth, amorphous solid with a characteristic conchoidal fracture, producing edges sharper than fine steel blades. The material is largely absent in Hawaii because the islands’ geology does not support its widespread formation. The vast majority of volcanic glass found there is chemically distinct from true obsidian, a difference stemming from the fundamental composition of the magma.
The Geological Requirements for True Obsidian
The formation of true obsidian relies on magma with a high concentration of silicon dioxide (silica), typically 65% to 80% of its composition. This high silica content makes the magma extremely viscous, a condition found in explosive volcanoes near continental subduction zones. The high viscosity inhibits atomic movement, preventing crystal structures from forming as the lava rapidly cools. This chemical makeup is necessary to produce the large flows of rhyolitic obsidian prized for tool-making.
Hawaii’s shield volcanoes are fed by a hot spot and erupt basaltic magma, which is low in silica and rich in heavier elements like iron and magnesium. Basaltic lava is highly fluid and low-viscosity, allowing it to flow great distances before cooling. This low-silica composition chemically prevents the formation of rhyolitic obsidian, explaining its virtual absence across the islands.
Volcanic Glass Materials Found in Hawaii
Since true obsidian is not prevalent, the Hawaiian Islands produce several types of volcanic glass from basaltic lava. One common form is tachylyte, a dark, opaque basaltic glass that forms the thin, glassy crust or rind on the surface of Pāhoehoe lava flows. Although chemically mafic, tachylyte’s rapid cooling still results in a glassy structure without significant crystal growth.
Two delicate forms of glass are named after the Hawaiian goddess of volcanoes, Pele. Pele’s Hair consists of fine, hair-like strands, often golden-brown, created when gas bubbles burst within a lava fountain, stretching the molten material into thin fibers as the wind carries them away. These threads are typically less than half a millimeter thick and accumulate in downwind areas.
Often attached to these strands are Pele’s Tears, small, teardrop-shaped or spherical droplets of black volcanic glass. These tears form when airborne particles of molten lava solidify into aerodynamic shapes before hitting the ground. Both Pele’s Hair and Pele’s Tears are scientifically categorized as basaltic glass, chemically distinct from the high-silica structure of true obsidian.
Uses of Local Volcanic Glass in Hawaiian History
Ancient Hawaiians (Kanaka Maoli) utilized the locally available volcanic glass, despite it being chemically different from high-quality obsidian. The glassy rind of lava flows offered the sharpest edges available from the local environment. Archaeologists found evidence that this material was used for various small, informal tools.
The naturally occurring sharp flakes served primarily as small scrapers or cutting implements for lightweight tasks, such as butchering birds or fine woodworking. Because the raw material was limited to thin rinds or small fragments, it did not support the manufacture of large, formally shaped tools like the projectile points and blades made from obsidian elsewhere.