Gadolinium is the sixty fourth element on the periodic table, giving it sixty four protons and electrons. Like the other rare earth elements, gadolinium is too reactive to be found free in nature and instead can be found in a number of minerals including monazite and bastnäsite.
The element is typically characterized as a transition metal, or sometimes as an inner transition metal. Given the sheer number of transition metals it is difficult to define any definite characteristics but, generally, transition metals are paramagnetic with more than one oxidation states. Also, metals typically (though not always) have high electrical conductivity as well as high density and high melting and boiling points.
Within the transition metals, gadolinium is classified as a lanthanide. All lanthanides are considered rare earth elements on the periodic table. Despite the name however, rare earth elements are not necessarily rare – they’re just notoriously hard to find in large enough quantities to be useful. Often found together, rare earth elements are difficult to separate.
A silvery-white, ductile, malleable metal, gadolinium has two major allotropes with a transformation temperature at 1235 °C. Naturally occurring gadolinium is composed of six stable isotopes and one radioisotope.
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