This rock type is usually named Jotnian sandstone, arkose or quartzite. The bulk of these stones are probably from the bottom of the Gulf of Bothnia (between Sweden and Finland) but some are from the Finnish and Swedish mainland as well.
This sandstone contains lots of feldspar. That’s why it is often described as arkose – a sandstone that contains at least 25% feldspar. The abundance of feldspar indicates that arkose is quite immature rock type – its travel distance from the source rock to the deposition location have been relatively short and the journey rapid.
In this particular instance it seems to be the case as well because in Western Finland our arkose is deposited in the fault bounded structural basin (Satakunta Formation). The maximum thickness of the sandstone formation is not known but it is probably well over one kilometer. The source material is the Svecofennian basement (1.9 billion years old). The arkose itself is approximately half a billion years younger. It is probably deposited as a fluvial sand (deposited by a running water).
Coarse-grained arkose. Pink grains are feldspar and gray ones quartz crystals. This rock sample was collected in the NW corner of Estonian mainland. The width of the view is 2 cm.
This post is a part of the Rocks from Fennoscandia series.
