PORPHYRY (BYTOWNITE) BASALT - Keswick, Cumbria
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460 million years old
Eycott Hill, Keswick, Cumbria
Conspicuous crystals of bytownite in basaltic lava from Eycott Hill in the Lake District where there are over 20 lava flows dating from the Ordovician period. The large crystals formed as molten rock cooled slowly in a magma chamber.
Conspicuous crystals of bytownite in basaltic lava from Eycott Hill in the Lake District where there are over 20 lava flows dating from the Ordovician period. The large crystals formed as molten rock cooled slowly in a magma chamber.
Bytownite is a variety of plagioclase feldspar and is close to labradorite in chemical composition. It was named from its occurrence at Bytown (now Ottawa), Canada.
Rocks like this that have large crystals in a groundmass of very small crystals are called porphyries, and the adjective porphyritic is used to describe them. This rock is sometimes polished to create small decorative items and has been given the name 'lakelandite'.
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Size: approx 8 x 4.5 x 3 centimetres
Weight: 167 grams
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