These are the elements from the 6th (lanthanide series) and 7th (actinide series) row in group 3 in the periodic system. They are metals with vaguely similar chemical properties and some quite fascinating uses in modern technology, hence are required in the production of various items. As their name implies they are very rare and difficult to obtain. Many rare earth elements can only be produced artificially because they are so unstable that they break up after fractions of a second. Those that have at least one stable isotope are not usually found in their pure form but have to be refined from so-called rare earths, rare minerals that tend to consist of several of these elements and isotopes at the same time which makes separation even more difficult. Some rare earth elements, like uranium and plutonium, are also considered basic construction materials (metals, light alloys, basic elements or complex compounds) because of their industrial uses.