GNEISS - over 3 billion years old - Greenland
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GNEISS
At least 3 billion years old
Kobberminebugt,
south of Ivittuut, Greenland
A good example of the metamorphic rock gneiss from Kobberminebugt (Danish for Coppermine Bay), a fjord in southwest Greenland. The rocks in this area date from the Archean Eon and are at least 3 billion years old.
This attractive specimen is from an old university collection and has been cut with a diamond saw and partially polished.
Gneiss (pronounced 'nice') is formed under the extreme conditions that exist beneath mountain ranges and in the collision zone between continental plates. The very high temperatures and pressures enable the rock to change completely and new minerals to crystallise. This rock may originally have been a sedimentary rock. The hot rock became soft as it approached melting point. If it had melted completely it would, on cooling, have become a granite.
The pale purple marks were made by a marker pen as a cutting guide.
Click on a picture for a larger image
Size: 11.5 x 6 x 5 centimetres
Weight: 584 grams