Obsidian in Pennsylvania

August 07, 2013

ObsidianIMG_0313 (2)

Photographer: Russell Losco; Russell's Web site
Summary Author: Russell Losco

The state of Pennsylvania is not known for volcanism. In fact, the last volcanic event in the area was approximately 201 million years ago and was associated with flood basalts of the Central Atlantic Magmatic Province -- from the first breakup of the supercontinent of Pangaea. This rifting stopped and the Gettysburg-Newark Basin was formed as a result. No obsidian from these eruptions has been found. However, in the Pittsburgh region, steel smelting produced large amounts of anthropogenic obsidian, such as pictured above. The steel making process involves heating a mixture of iron ore, limestone and coke (distilled bituminous coal) to temperatures beyond what is needed for the natural formation of obsidian. The impurities in the melt rise to the top and are decanted off and cooled, resulting in slag. I was born and raised in the Pittsburgh area and remember watching molten slag being dumped down the banks of the Ohio River on a regular basis. The molten slag looked like lava as it flowed down the banks and lit the sky up for miles with its orange glow. The specimens pictured above were collected in the town of Baden, where due to decades of steel production, the slag is being mined for use as aggregate. Photo taken on June 21, 2013.

Photo details: Camera Maker: Apple; Camera Model: iPhone 4; Focal Length: 3.9mm (35mm equivalent: 35mm); Aperture: f/2.8; Exposure Time: 0.0083 s (1/120); ISO equiv: 100.