Mineral Species: Quartz var. Mahogany Obsidian

Chemical Formula: SiO2

Chemical Name: Silicon Dioxide

Mineral Class: Tectosilicates

Mineral Notes:  Obsidian is a type of naturally-occurring silicate glass formed as an extrusive igneous rock. It is produced when felsic lava erupts from a volcano cools rapidly through the glass transition temperature and freezes without sufficient time for crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid. Because of the lack of crystal structure, obsidian blade edges can reach almost molecular thinness, leading to its ancient use as projectile points, and its modern use as surgical scalpel blades.

Description: A black and mottled brown varierty of Obsidian also known as Mountain Mahogany. The brown clour is due to the inclusion of iron in the volcanic glass. One side of the specimen shows a conchioidal fracture zone, which is a very characterisitc property of Obsidian. A very aesthetic specimen.

Location: Obsidian Tank, Coconino Co., Arizona, USA.