Obsidian, caused naturally when lava cools very quickly, is what type of substance?
Obsidian Obsidian Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. Obsidian is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where the chemical composition (high silica content) induces a high degree of viscosity and polymerization of the lava. The inhibition of atomic diffusion through this highly viscous and polymerized lava explains the lack of crystal growth. Obsidian is hard and brittle and therefore fractures with very sharp edges. In the past it was used to
Ice-marginal lava flow ice sheet's margins. Initially, the lava flow is like any other but when the lava reaches the margins of an ice sheet, the front of the lava flow cools very quickly and thus, forms a barrier (Figure 1). Behind this barrier, the lava begins to pool, ceasing the contact between the hot lava and cold ice. The barrier is left behind as the ice retreats, leaving a thick lava front, which is just a large, steep, and unstable cliff face. The Barrier A fantastic example of a natural lava dam formed from an ice-marginal lava flow is a phenomenon aptly