Stone Type: Rhyolite

Rhyolite Flake, wedging initiation, Australia

Rhyolite is an extrusive igneous stone formed in volcanic eruptions where granitic magma reaches the surface.  It tends to be very viscous and, during eruptions, is more likely to be ejected as pyroclastic rock rather than lava flows (which most often form basalt).  Rhyolite has a high silica content and, depending on how quickly it cools, it can be relatively fine-grained and suitable for making stone tools.  If rhyolite cools very rapidly, obsidian is formed.  

Kolea stone

Kōlea Stone

Flake, wedging initiation, Australia


Clovis platter biface Maine

Bifacial Core

Gorget broken NC