It's Elemental

The mineral gadolinite ((Ce, La, Nd, Y)₂FeBe₂Si₂O₁₀), discovered in a quarry near the town of Ytterby, Sweden, has been the source of a great number of rare earth elements. In 1843, Carl Gustaf Mosander, a Swedish chemist, was able to separate gadolinite into three materials, which he named yttria, erbia and terbia. As might be expected considering the similarities between their names and properties, scientists soon confused erbia and terbia and, by 1877, had reversed their names. What Mosander called erbia is now called terbia and visa versa. From these two substances, Mosander discovered two new elements, terbium and erbium. Today, terbium can be obtained from the minerals xenotime (YPO₄) and euxenite ((Y, Ca, Er, La, Ce, U, Th)(Nb, Ta, Ti)₂O₆), but is primarily obtained through an ion exchange process from monazite sand ((Ce, La, Th, Nd, Y)PO₄), a material rich in rare earth elements that typically contains as much as 0.03% terbium.

Terbium is used to dope some types of solid-state devices and, along with zirconium dioxide (ZrO₂), as a crystal stabilizer in fuel cells that operate at high temperatures.

Terbia, the renamed material that Mosander discovered in 1843, is terbium oxide (Tb₂O₃), one of terbium's compounds. Terbia can potentially be used as an activator for green phosphors in television tubes. Sodium terbium borate, another terbium compound, is used to make laser light.