[2][3] The dykes of the complex consist of carbonatite and alkaline rocks such melilite and sövite.
[3] It has been proposed that both the Fen Complex in Southern Norway and the Alnö Complex formed as consequence to mild extensional tectonics in the ancient continent of Baltica following the opening of the Iapetus Ocean.
[5] Harry von Eckermann published a landmark study on the Alnö Complex in 1948 correctly claiming a magmatic origin of carbonatite, albeit his finds were only widely accepted after the Ol Doinyo Lengai eruption of carbonatite lava in the 1960s showed contemporary evidence on the existence of such magmas.
[6] As result of decreased foreign trade during World War II apatite was mined from the carbonates of Alnö Complex from 1943 to 1945.
[7] While the separation process had improved in 1945 the end of the war the same year meant that apatite mining became unprofitable.