Norwegian thulite & larvikite

One rock is named after a Norwegian town and the other after the mythical island at the edge of the world.

Larvikite takes its name from the town of Larvik, and it is the county stone of Vestfold. The University of Oslo's Natural History Museum describes it as a variety of monzonite, a plutonic rock formed by melt solidifying deep underground. Along the coast it weathers into the smooth rounded slabs Norwegians call svaberg. It is coarse-grained and dark grey, bluish or greenish, and sometimes carries a beautiful blue shimmering play of colour, which is exactly why it is wanted as facade and monument stone. Where it is red instead it goes by another name, Tonsbergite.

The composition is a variety of augite monzonite: rhomb-shaped feldspar, barkevikite, titanium-augite and the black mica lepidomelan, with smaller amounts of nepheline, iron-rich olivine and quartz sometimes present. The feldspar is a fine intergrowth of potassium feldspar within plagioclase, and before anyone understood that, the rock was classified as a syenite.

For a collector the interesting part is the coarse stuff. Rare minerals turn up in the coarser streaks and in the pegmatite dykes cutting through it.

The scale is hard to picture. Larvikite covers roughly 1,700 square kilometres of the Oslo region, especially between Tonsberg and Larvik, which is almost a third of the total area of all the Permian plutonic rocks in the Oslo field.

Thulite is the other half of this pin and a very different thing. It is a rose-red, manganese-bearing variety of the mineral zoisite, hardness 6.5 to 7, used as a gemstone and for ornamental objects, and some call it Norway's national stone. It is particularly known from Leksvik in Trondelag, and at Lom it occurs alongside red manganese-bearing epidote in quartzite. It was first described from Sauland in Telemark in 1823, and the name comes from Thule.

Quarries are PRIVATE/industrial; material is widely sold.