Larvikitt

You can find it in many major cities, and it is highly sought after for its beautiful shimmering blue color. When you see it elsewhere in the world, you can be sure that it comes from the Larvik area of Norway. Larvikite is also used as another type of decorative stone, such as tiles, countertops, benches, or gravestones. In England, larvikite is even commonly used as a bar counter stone! In 2008, the rock was designated as Norway’s national rock.

Colors

The color of the rock can vary from light gray to very dark gray, almost black, but with distinct blue crystals. Not all larvikite occurrences display this fine blue shimmer; the best examples are found in the area between Tjølling and Tvedalen. Larvikite actually exists in many different varieties, with slightly different chemical compositions, and this is clearly visible in the rock itself.

Geological Properties

Larvikite consists almost entirely of feldspar, and it is a special effect in the feldspar crystals that gives it the blue color. This effect is called the “Schiller effect,” and it is believed to originate from ternary feldspar (feldspar containing calcium, sodium, and potassium). Larvikite is an igneous (magmatic) rock, formed deep in the earth, at about 30 kilometers’ depth. Far below the surface, the magma cooled and solidified while large crystals formed. This happened in the Early Permian, about 298–293 million years ago, during the breakup of the supercontinent Pangea and the eventual formation of the Oslo Rift.

Afterward, the solidified rock was uplifted to the earth’s surface by various geological processes. Conditions at the surface are different than several kilometers down, and the crystals that once formed are no longer stable up here. Microscopic changes have occurred in the feldspar, creating the blue shimmer when the rock is cut correctly.

It is not simply a matter of finding high-quality larvikite and cutting a nice piece; it takes skilled craftsmanship to extract blocks, assess their quality, and decide which direction to cut the block so the color is shown at its best

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Variations

At some localities, larvikite may appear as a homogeneous rock. However, the large area of magma that later solidified shows marked layering. Sometimes, as at Ula, this layering is very clear, but otherwise, the size of the locality and how the larvikite is exposed determines how visible the layering is. Although feldspar is the main mineral in larvikite, the rock also contains some olivine, clinopyroxene, amphibole, biotite, magnetite, and apatite. Occasionally, a little nepheline can also be found. Some of these minerals are dark, while feldspar and nepheline are lighter, and variations in the content of light and dark minerals create the layering