Rainbow Obsidian

[gregszybala]

Dense volcanic glass, usually black in color and rhyolite in composition.
Obsidian with multicolored iridescence caused by inclusions of magnetite nanoparticles.
This piece from Davis creek in the Warner mountains of Northern California

Read more at http://www.geologyin.com/2017/08/cal...LWPmUdZfzRl.99