atomic number 58, Ce, cerium - a ductile gray metallic element of the lanthanide series; used in lighter flints; the most abundant of the rare-earth group

atomic number 63, Eu, europium - a bivalent and trivalent metallic element of the rare earth group

atomic number 60, Nd, neodymium - a yellow trivalent metallic element of the rare earth group; occurs in monazite and bastnasite in association with cerium and lanthanum and praseodymium

atomic number 59, Pr, praseodymium - a soft yellowish-white trivalent metallic element of the rare earth group; can be recovered from bastnasite or monazite by an ion-exchange process

atomic number 62, samarium, Sm - a gray lustrous metallic element of the rare earth group; is used in special alloys; occurs in monazite and bastnasite

atomic number 65, Tb, terbium - a metallic element of the rare earth group; used in lasers; occurs in apatite and monazite and xenotime and ytterbite

atomic number 90, thorium, Th - a soft silvery-white tetravalent radioactive metallic element; isotope 232 is used as a power source in nuclear reactors; occurs in thorite and in monazite sands

atomic number 69, thulium, Tm - a soft silvery metallic element of the rare earth group; isotope 170 emits X-rays and is used in small portable X-ray machines; it occurs in monazite and apatite and xenotime

atomic number 70, Yb, ytterbium - a soft silvery metallic element; a rare earth of the lanthanide series; it occurs in gadolinite and monazite and xenotime

mineral - solid homogeneous inorganic substances occurring in nature having a definite chemical composition