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.

HornfelsTS0

 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%)

 

HornfelsTS1

Back to contact metamorphic rocks

Thin-section images provided by our partners at ImageMatrix.

 
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