Manger

Various mangeritic rock types are found several places in Hordaland, but Manger is what geologists call the "type locality". This intrusive rock type resembles granite, and stone-workers would probably call it a dark granite. Similarly as granite, mangerite contains potassium feldspar and plagioclase feldspar. Mangerite is nonetheless more basic (alkalic) than normal granite, and is richer in dark minerals such as pyroxene, hornblende and dark mica (biotite).

If we examine potassium feldspar under a microscope, we will see some characteristic, worm-like stripes that geologists refer to as "perthite structures". The "worminess" comes from a sodium-rich variety of feldspar that precipitated out as the rocks cooled about a billion years ago.

On Radøy, the mangerites are found in an area that stretches north- and eastwards from Manger. In this area, one finds mounds that stick up in the terrain. Other rock types in this family are also found other places in the Bergen Arcs, in the high mountains from Voss to Jotunheimen, in Lofoten and in the Egersund area. Some places the mangerites are rich in iron ores, such as ilmenite (titanium iron), magnetite or hematite. Attempts have been made to mine these minerals by Selfallet on the west side of Mangersvågen, but without much success.

On a global basis, mangerite bedrock is uncommon. Therefore, the Bergen Museum has used mangerite as a trade-object, in order to increase its collections of minerals from other parts of the world.