Garnet peridotite from Fjørtoft island

Garnet-kyanite gneiss (12 cm) from Vågholmen, Fjørtoft island

Fjørtoft island is part of The Western Gneiss region of Norway. This region stretces for about 300 km from Sognefjorden to Trondheimsfjorden. At the north east coast of the island there is a rock structure containing garnet-kyanite gneisses, kyanite eclogite and garnet peridotite. Some of these rocks contain minerals like coesite and micro diamonds, indicating that they have been exposed to extremely high pressures and temperatures. Diamond and coesite are Ultrahigh pressure minerals (UHP) and occur as microinclusions in other minerals in the gneisses and eclogites of Fjørtoft island.

Micro diamonds were first found at Fjørtoft in 1993 in garnet-kyanite gneiss samples from the northeast coast of the island.
At northwestern Fjørtoft there is a pod of garnet peridotite which in 2002 also was shown to contain micro diamonds.

More information of the geology of Fjørtoft island: NGU, Trondheim

Harald Dyrkorn 2100 Skarnes
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