Samarskite is a radioactive rare earth mineral series which includes samarskite-(Y), with the chemical formula (YFe3+Fe2+U,Th,Ca)2(Nb,Ta)2O8[3] and samarskite-(Yb), with the chemical formula (YbFe3+)2(Nb,Ta)2O8.

[5] Samarskite crystallizes in the orthorhombic – dipyramidal class as black to yellowish brown stubby prisms although it is typically found as anhedral masses.

Specimens with a high uranium content are typically metamict and appear coated with a yellow brown earthy rind.

It occurs in association with columbite, zircon, monazite, uraninite, aeschynite, magnetite, albite, topaz, beryl, garnet, muscovite and biotite.

[4] Samarskite-(Yb) was first described in 2004 for an occurrence in the South Platte Pegmatite District, Jefferson County, Colorado.