Finland – Sandatlas

The Fennoscandian shield is located in Finland, Sweden, and NW Russia. Part of it is in Norway also. Shields are extensive areas of exposed basement rocks. Basement rocks are hard crystalline rocks that usually have formed during orogenies. The lithology of shield areas is generally versatile and very interesting.

Shield is tectonically stable area, just like platforms which are covered by sedimentary rocks. Crystalline basement is exposed in shield areas but that doesn’t mean that these rocks are outcropping everywhere. They are still mostly covered with loose sediments, soil, and vegetation but there are no sedimentary rocks on top of the basement. Well known shield areas are located in Canada, Fennoscandia, Australia, and several other places.

Here I am focusing on the Fennoscandian shield. It is close to where I live — Estonia. My home country is located on the sedimentary platform but the Scandinavian shield is very near. Continental glaciers that reigned here mere 12,000 years ago brought lots of boulders with versatile origin and composition.

Whenever I write a post about the rock from the Fennoscandia, I also add it here. These posts may be about rocks that were brought to Estonia by the glacier but often they are about the Fennoscandian rocks in their natural birthplace.

	Mylonite from Estonia	Metamorphic rock with ‘eyes’ or augens.
	Most famous gneiss in the Internet	The story of a gneiss hand sample. I am not sure where this rock is from but there is a high probability that it is from the Fennoscandian shield, most likely from Karelia where I have seen similar gray gneisses.
	Rapakivi granite	Rapakivi is a special type of granite with an interesting texture.
	Ruskeala marble	Marble from Ruskeala quarry in Karelia.
	Anorthosite	Anorthosite is famous for its play of colors. Find out what causes it.
	Jotnian sandstone	This feldspar-rich rock is usually named either Jotnian sandstone, quartzite, or arkose.

Overview and images of sandstone as a rock type are here: Sandstone

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 – 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.