The Petrographic Collection

The collection is divided into the following units:

A systematic collection of magmatic and metamorphic rocks, principally with European examples.

A reference collection illustrating the geology in areas with magmatic and metamorphic rocks; including

Collections from Denmark (especially Bornholm), the Faroe Islands, Iceland and Greenland, collected during the more than 200 years the museum has existed. Many of these collections are of considerable interest because of their history.

Collections illustrating the conditions in other regions where the research has been of special importance to the understanding of the magmatic and metamorphic processes.

The top left photo shows:
Thick lava benches of igneous rock basalt build up up the mountain Giesecke's Monument on the Nuussuaq peninsula in West Greenland. The individual layers were formed by very large lava eruptions (individually of many cubic kilometres) about around 60 Ma. The beautiful massif was formed by erosion in the Quaternary.

A documentation (original) collection with magmatic and metamorphic rocks, mainly from Denmark, the Faroe Islands and Greenland. The material has formed the basis of scientific research papers published by Danish and foreign scientists. An important part of the collection is the material deposited by the Geological Survey of Denmark and Greenland according to an agreement between the institutions.

Rock samples from the Petrographic Collection may be borrowed for scientific research, education and exhibitions, mainly by other museums and institutes of higher education.

The Petrographic Collection can offer the following collections for exchange: Archaean rocks from the Nuuk-area in western Greenland; alkaline, magmatic rocks from the Proterozoic Ilímaussaq intrusion in southern Greenland; Tertiary volcanic rocks from the Faroe Islands and western Greenland (Disko-Nuussuaq); indicator boulders from the Quaternary glaciation of Denmark.

Micro photo of thin section of the quenched margin at a 60 Ma. basalt pillow from the south coast of Disko in West Greenland.
The ca. 1200º hot silicate magma was quenched by contact with water to natural glass (light brown areas gl). Within the glass are seen phenocrysts of the three main minerals in the rock type basalt: olivine (ol), pyroxene (px) and plagioclase (pl). The phenocrysts are about 1 mm in size.

At the entrance to the Geological Museum is seen a large block weighing many tons of native iron from Uiffaq on the south coast of Disko. A smaller block from the same locality is situated on the left side of the stone staircase leading to the exhibition area. These blocks were discovered where a basalt dyke is exposed on a beach by the Swedish professor A.E. Nordenskiöld in 1870. A few years later they were under extremely difficult circumstances lifted onboard a ship from the Swedish navy and carried to Sweden where the largest iron block is exhibited. The discovery was a geological sensation at the time, when geologists first believed the blocks to be iron meteorites. Later it was proved that the iron formed at about 60 Ma. by natural reduction by reaction between basalt magma and organic carbon from sediments. The iron blocks are affected by sea water and would crumble to rust in a few years if exhibited indoors. On the other hand, they are preserved excellently outdoors, but they do not like road salt.

Vehmaa granite from the Precambrian of southern Finland. The light reddish mineral is potassic feldspar, the dark grey mineral is quartz. The rock is an excellent face stone.

Granite from the Rapakivi Group from the Precambrian of southern Finland.

Granite is a SiO₂-rich igneous rock solidified several kilometres beneath the land surface of that time. The rock consists of the minerals potassic feldspar, plagioclase, quartz and biotite.

Curator:

Asger Ken Pedersen