Larvikite is well known throughout the world, since it is a very popular ornamental exterior stone in buildings.
You see larvikite in many larger cities, and it is much sought-after, with its beautiful shimmering blue color. When you see it elsewhere in the world, you can be sure it comes from the Larvik area of Norway. Larvikite is also used in other ways as ornamental stone, in tiles, worktops, benches or gravestones. In England one even sees Larvikite used as counters in bars! In 2008 Larvikite was named Norway’s national rock.
The color of the stone can vary between light gray and quite dark gray, nearly black, but with clear blue crystals. Not all of the larvikite occurrences show this fine blue shimmer; the best examples come from the area between Tjølling and Tvedalen. Larvikite comes in many different varieties, reflecting small differences in the chemical composition. And this is clearly seen in the rocktype!
Larvikite is comprised nearly entirely of feldspar, and it is the special effect of the feldspar crystals that give it its blue color. This effect is called the "Schiller effect", and one suspects that it originates from the ternary feldspar (feldspar that contains calcium, sodium and potassium). Larvikite is an igneous rock (magmatic rocktype), that is formed at depth, about 30 kilometers deep. Far below the surface the magma cooled and hardened as large crystals formed. This occurred in Early Permian time, about 298-293 million years ago, in association with the break-up of the super continent Pangea and eventual formation of the Oslo Rift. Afterward, the hardened rock was carried up to the earth’s surface by a variety of geological processes. The conditions on the earth’s surface are different from those at several kilometers’ depth, and the crystals that were formed at depth are no longer stable up here. Microscopic changes have occurred in the feldspar, and this creates a blue shimmer when the rock is cut correctly. It is in fact not just a matter of finding larvikite of good quality and then cutting off a pretty bit – it requires good handwork to remove blocks, evaluate their quality and then decide which way to cut the block so that the color will shimmer most beautifully.
In some localities the larvikite can seem like a homogeneous rock type. But,the large area of magma that subsequently hardened shows a noticeable layering. Sometimes, as near Ula, this layering is very clear, but otherwise it is the size of the locality and how the larvikite is exposed that determines the clarity of this layering. Even though the main mineral in larvikite is feldspar, the rock type also contains some olivine, clinopyroxene, amphibole, biotite, magnetite and apatite. Sometimes there is also a little nepheline present. Some of these minerals are dark, but feldspar and nepheline are lighter, and it is the variations in the content of the light and dark minerals that causes the layering.
Gea Norvegica Geopark
Gea Norvegica Geopark is the first European Geopark in Scandinavia. It is located in southeastern Norway, in the counties of Vestfold and Telemark.
The Geopark is limited by the administrative areas of the muncipalities Kragerø, Bamble, Porsgrunn, Skien, Nome, Siljan and Larvik