Gadolinium (Gd) is a chemical element with atomic number 64. It is a rare-earth metal that is part of the lanthanide series. Gadolinium is a silvery-white metal that is malleable, ductile, and has a high melting point. It is the tenth most abundant rare-earth element and is found in several minerals, including gadolinite, monazite, and bastnäsite. Gadolinium is used in a variety of applications, including:

* Alloys: Gadolinium is used as an alloying element in steel, aluminum, and magnesium alloys. It improves the strength, hardness, and toughness of these alloys.

* Magnetic materials: Gadolinium is used in the production of magnetic materials, such as gadolinium gallium garnet (GGG) and gadolinium scandium gallium garnet (GSGG). These materials are used in a variety of applications, including medical imaging, telecommunications, and lasers.

* Phosphors: Gadolinium is used in the production of phosphors, which are materials that emit light when exposed to radiation. Gadolinium-based phosphors are used in a variety of applications, including fluorescent lamps, plasma displays, and lasers.

* Contrast agents: Gadolinium-based contrast agents are used in magnetic resonance imaging (MRI) to enhance the visibility of certain tissues and organs. These contrast agents are injected into the bloodstream and help to produce clearer and more detailed images.

Gadolinium is a relatively safe material, but it can cause side effects in some people. These side effects can include nausea, vomiting, headache, and dizziness. Gadolinium-based contrast agents can also cause a rare condition called gadolinium deposition disease, which can lead to skin lesions, joint pain, and other symptoms.