This molten earth origin is what classes rainbow obsidian as an igneous rock. Lava destined to become obsidian cools rapidly once on the surface and, thanks to its viscous nature, is also below ...

Extrusive igneous rocks are formed by magma that has erupted onto the surface as lava and then cooled quickly. Obsidian is an example of an extrusive igneous rock. Obsidian has crystals which are ...

Obsidian, a gemstone also known as volcanic glass, is widely distributed in the Southwest. It is an extrusive igneous rock comprised of feldspar and quartz, endemic to volcanic regions.

Sodalite forms in igneous rocks that crystallized from sodium-rich, silica-poor magmas. That’s how it got its name—soda + lithos, or “sodium stone," according to Rock Your World gem & art ...

Intrigued, Johnson studied up on the local geology, finding that this is not the first time these interesting igneous rocks had been spotted. As far back as 1899, such obsidian and minerals had ...

The igneous rock obsidian has long been a useful reference for archaeologists to piece together the past, given Maori used it for a range of tools and activities. University of Auckland researcher ...