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Plane polarised light. Garnet mica schist from hornfels zone of the Skiddaw Slates, the inner metamorphic aureole of the Skiddaw Granite,, 3km. west of Scales Tarn, Blencathra. The specimen was taken from about 6cm from the actual contact with the granite at Sinen Gill, grid ref. NY301281 |
Cross polarised light. The large crystal is a garnet, about 0.5mm in diameter. Having a cubic crystal structure it is isotropic, therefore opaque under crossed polars. Most of the specimen consists of muscovite mica (bright interference colours), biotite mica (brown) and quartz (grey interference colours). The sub-parallel alignment of the micas, especially seen towards the bottom right, is a reflection of the original slaty cleavage. |
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The picture on the left was taken in Sinen Gill and shows the contact between the underlying Skiddaw Granite, the lighter coloured rock where the girl is standing and the overlying darker metamorphosed Skiddaw slates. The specimen for the thin section was taken about 6cm above the hammer on the left. |
