Three group 3 elements occur naturally&colon; scandium, yttrium, and either lanthanum or lutetium. Rubidium, strontium, yttrium, zirconium, and niobium have no biological role. Thulium is often found with minerals containing yttrium and gadolinium. Cyclooctatetraene forms organometallic complexes with some metals, including yttrium, lanthanides, and actinides. The properties of scandium compounds are intermediate between those of aluminium and yttrium. Trace elements, strontium and yttrium, were detected. Ytterbium is often the most common substitute in yttrium minerals. By reacting the resulting yttrium oxide with hydrogen fluoride, yttrium fluoride is obtained. There are two atoms of Barium for each atom of Yttrium. Especially catalyst metals like nickel, cobalt or yttrium may be of toxicological concern. Yttrium oxide is used as the stabilizer. Yttrium iron garnet (YIG) spheres can act as tunable microwave resonators. He detected it as an impurity in yttrium oxide, YO. The dopant levels used range between 0.2% and 30% of replaced yttrium atoms. Yttrium compounds are used as a catalyst for ethylene polymerization.