Magnesium is a common alkaline earth metal used mainly in the production of low-density alloys. It does not occur in nature in the elementary state, only in the form of compounds. Economically its most important mineral is magnesite, which is a magnesium carbonate (MgCO3). The largest magnesite deposits in the world occur in the Slovake Ore Mountains, the most significant of which are Hnúšťa, Ratkovská Suchá, Jelšava, Lubeník, Burda and Košice.
In the picture: Polished section of magnesite, Košice (Slovakia). Size: 7 cm. Photo by Géza Kulcsár.