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Title: rhomb porphyry
Item Name: Rock


This rock consists of a mass of fine-grained red groundmass in which float the paler coloured prisms (rohmbs) of feldspar. The feldspar has started to form crystals as the magma cooled very slowly, but then it has been cooled more rapidly, and the earlier crystallisation process has been 'frozen'. Rock specimens like this are valuable in ascertaining where ice flows were coming from during the Pleistocene Period. In this case it is almost beyond reasonable doubt that the rock originated in Scandinavia, probably Norway. This specimen will have been washed out of boulder clay deposits which drape the cliffs in the Flamborough area, or possibly from offshore deposits.

Measurements: L: 18cm
ID_Number: ERYMS : 2006.67