BOILING POINT: 2,720°C
DENSITY: 8.803 g/cm 3
MOST COMMON IONS: Ho 3+
A member of the lanthanide , or rare earth, series of elements, holmium is a gray, somewhat shiny, soft metal . It is usually found in minerals containing several of the lanthanides. Because the rare earths all have the same outer electron shell configuration (6s 2 ), their chemical properties are very similar, making it difficult to separate them from one another in the minerals in which they are usually complexed. They are best separated via repeated ion-exchange purification, a process developed in the United States during the 1940s. Although several of the rare earths are used in industrial chemical processes and in metal alloying, holmium has few commercial uses.
Holmium is easily oxidized, forms a wide variety of compounds, especially salts, and forms alloys with other metals. The pure metal has unusual magnetic properties that become apparent at low temperatures. In pure holmium the electron spins (which produce the magnetism) are aligned—not in parallel fashion as in iron, but in a manner such that helices are formed. Holmium has been used to make parts for magnets that produce intense magnetic fields. The isotope 165 Ho has an unusual football-shaped nucleus, which has been the focus of several important experiments investigating the nature of nuclear forces. In one atom the holmium electrons interact with the nucleus as if they produce a magnetic field of 740 tesla. This "hyperfine field" is one of the strongest such fields found in nature.
David G. Haase
Spedding, Frank Harold, Jr., and Daane, Adrian Hill, eds. (1961). The Rare Earths. New York: Wiley.