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15 June 2011
Obsidian hunting in the Jemez Mountains
This past weekend I took a day to go revisit the Valles Caldera. While I was wandering the trails, I decided to do a little “rockhounding”. Geologists are often notorious for their rock collections, and I felt like mine was missing something that no volcanologist should be without: Obsidian.
Obsidian is basically volcanic glass – the result of lava cooling so quickly that it doesn’t have time to develop crystals. Pure glass is basically SiO2, and obsidian tends to form from rhyolitic magmas (which already have a high percentage of SiO2, typically greater than 68%). “Heavy” minerals in the obsidian (such as iron and magnesium) make the glass dark, and (depending on their oxidation state) can give it reddish or greenish hues.
Jessica Ball is a volcanologist at the U.S. Geological Survey, researching volcanic hydrothermal systems and stability, and doing science communication for the California Volcano Observatory. She previously worked at the Geological Society of America's Washington DC Policy Office, learning about the intersection of Earth science and legislative affairs. Her Mendenhall postdoc and PhD focused on how water affects the stability of volcanoes, and involved both field investigations and numerical modeling applications. Her blogging covers a range of topics, from her experiences in academic geosciences to science outreach and communication to her field and lab work in volcanology.