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When it was decided that the Gottesman Hall of Planet Earth would be designed around huge rock samples, one obvious choice for the volcano section of the hall was obsidian. This glossy black rock is a dramatic product of volcanism, which is related to plate tectonics. The processes involved in the movement of the Earth's plates, that form ocean basins, build mountains, and cause continents to move and grow, are the same processes that cause volcanism.
Shiny obsidian is unique among volcanic rocks. It cools so quickly when it erupts from a volcano, that there is no time for crystals to form, so it has a smooth, glassy appearance. It is also unusually rich in SiO2, an important component of rocks in general. Obsidian is known as volcanic glass, and although it has a somewhat different make-up than the glass in a window pane its chemical composition is high in silica, just like window glass.
Dr. Ro Kinzler was given the charge of collecting a two-ton obsidian boulder for the exhibition. From her office in New York City, she carefully planned her expedition. First, she organized a meeting with geologist Dr. Julie Donnelly Nolan, a United States Geological Survey (USGS) expert on Medicine Lake Volcano in northeast California. Then, she contacted local pumice quarry owners Glenn and Heidi Malby, who agreed to act as guides. Ro also lined up a videographer and a photographer to document the collection process, and arranged for a flatbed truck to ship the selected specimen across the country.
Years earlier, while working on her master's degree in geology, Ro studied the area around Medicine Lake Volcano, the largest in volume of the Cascade Range volcanoes. The volcano's name came from a lake in its crater, Medicine Lake, which was used by the local tribes.
When Ro thought of a good place to find a large piece of obsidian, she immediately remembered Glass Mountain. This area, part of the Medicine Lake Volcano, was a well-known obsidian site, and had long been used by the local Modoc Indians as a source of the sharp rock for arrowheads and tools. Besides obsidian, the area held a wide variety of other volcanic rock types, ranging in
in chemical composition from light-colored, silica-rich rhyolite and shiny black obsidian to black, silica-poor basalt.
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