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CategoryOxide minerals
(repeating unit)
REENbO4 (REE: rare-earth element)
Strunz classification7.GA.05
Crystal systemTetragonal
Crystal classDipyramidal (4/m)
H-M symbol: (4/m)
Space groupI41/a
Formula mass245.81 g/mol (Y)
ColorBlack, black, brown, gray, yellow
Crystal habitMetamict – mineral originally crystalline, now amorphous due to radiation damage
FractureSubconchoidal – fractures developed in brittle materials characterized by semi-curving surfaces
Mohs scale hardness5.5–6
Density4.3–5.8, average = 5.05
Refractive index2.05–2.19, isotropic
Other characteristicsNonmagnetic, non-fluorescent, not radioactive

Fergusonite is a mineral comprising a complex oxide of various rare-earth elements. The chemical formula of fergusonite species is (Y,REE)NbO4, where REE = rare-earth elements in solid solution with Y. Yttrium is usually dominant (the species fergusonite-(Y)), but sometimes Ce or Nd may predominate in molar proportion (species fergusonite-(Ce) and fergusonite-(Nd)). All the other rare-earth elements are present in subordinate amount, and tantalum substitutes for some of the niobium. There are Fergusonite-beta-(Nd), Fergusonite-beta-(Y), Fergusonite-beta-(Ce) too, but they are classified as 4.DG.10 in the Nickel–Strunz system. The mineral has tetragonal crystal symmetry and the same structure as scheelite (calcium tungstate, CaWO4), but can be metamict (amorphous) due to radiation damage from its small content of thorium. It is found as needle-like or prismatic crystals in pegmatite. It was named after British politician and mineral collector Robert Ferguson of Raith (1767–1840).[2]

See also[edit]


  1. ^ Fergusonite-(Y) Mineral Data. Webminerals.
  2. ^ Robert Ferguson of Raith. University of Edinburgh.