Hornfels in thin-section
To see what some rocks are made of geoscientists make thin-sections. Yes, they are really thin slices of rock!
A thin-section is about 0.33 of a millimetre thick. Most minerals become transparent or translucent when they are that thin so we can easily look at them under a light microscope an see what size they are how they are arranged inside the rock.
The images below are photographs of a thin section taken from the same hornfels shown on the previous page. The image is about 40mm wide so each mineral grain you can see in the thin-section is tiny, much too small to see without a microscope.
The first image is taken with plain light. You can clearly see a variety of mineral grains.
The second image (below) is taken with a special polarising light microscope. This enables us to see the optical properties of each mineral - a bit like a finger print, each mineral has its own characteristics. From this we know that this hornfels contains
- quartz (50–60%)
- feldspar (20–30%)
- carbonate "spots" (5–10%)
- muscovite (5–10%)
- opaque minerals (<5%)
Back to contact metamorphic rocks ⇑
Thin-section images provided by our partners at ImageMatrix.
|Minerals||Rock Cycle||Igneous Rocks||Sedimentary Rocks||Metamorphic Rocks|
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