Rocks let light shine through

The geology department at Castleton State College is one of the smaller programs in the school, and because of how most people feel about rocks, it isn’t hard to imagine why.
But to Tim Marshall, a geology student at Castleton, what many people think of as just a rock is a tiny vault of information waiting to be released in a prism of colors.
In a project led by professor Tim Grover, Marshall and other students of the geology department are conducting a study using rock samples from the nearby Adirondack Mountains in the Shelving Rock Quadrangle in the town of Fort Ann.
“I really enjoyed hiking the ‘dacks with Tim this summer. It really allowed us to apply our knowledge in the field,” said Alex Clodgo, a fellow geology student and Marshall’s assistant this past summer.
Marshall and Clodgo collected the samples during a summer work study to help create a geologic map of the area to aid further research about how the foundations of our area were created.
Using a diamond and corundum tipped saw, the researchers cut these rock samples into incredibly thin sections averaging about 35 micrometers thick – or about the width of a human hair.
With this vault cracked open, Marshall can now use an electric microprobe to force light through the rock.
Using different wavelengths of light and measuring the refraction within the rock can tell Marshall about the mineral composition of it and the properties of those minerals. It also releases a kaleidoscope of different colors.
“Looking at it on a small scale can give you hints at the larger scale,” said Marshall.
This technique can also hint at the temperature and pressure conditions of where the rock was formed or “metamorphosed.”
“The rock samples are analyzed … to determine the mineral composition and to date the rock at the time of metamorphism and deformation,” Grover said in an interview before break.
With that information, researchers like Grover can make better hypotheses about the composition of the layers of bedrock within the quadrant.
This allows people to understand how the Adirondacks were formed by different planes of minerals interacting with one another to form the landscape we see today because every rock is a small piece of geologic record, Grover said.
Marshall and Grover will be back in the Adirondacks this summer working with fellow geology majors on this continuous project.
“I am radiating stoke about interning again this summer,” Marshall said.

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