Fergusonite
Encyclopedia
Fergusonite is a mineral comprising a complex oxide of various rare earth elements. The chemical formula of fergusonite species is (Y,RE)NbO4, where RE = 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 element
Rare earth element
As defined by IUPAC, rare earth elements or rare earth metals are a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium...

s are present in subordinate amount, and tantalum
Tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as tantalium, the name comes from Tantalus, a character in Greek mythology. Tantalum is a rare, hard, blue-gray, lustrous transition metal that is highly corrosion resistant. It is part of the refractory...

 substitutes for some of the niobium
Niobium
Niobium or columbium , is a chemical element with the symbol Nb and atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite...

. There are Fergusonite-beta-(Nd), Fergusonite-beta-(Y), Fergusonite-beta-(Ce) too, but they are classified as 04.DG.10 in the Nickel-Strunz
Strunz classification
Nickel–Strunz classification is a scheme for categorizing minerals based upon their chemical composition, introduced by German mineralogist Karl Hugo Strunz in his 1941 Mineralogische Tabellen. The 4th edition was edited by Christel Tennyson too . It was followed by A.S...

 system. The mineral has tetragonal crystal symmetry and the same structure as scheelite
Scheelite
Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws...

 (calcium tungstate, CaWO4), but can be metamict (amorphous) due to radiation damage from its small content of thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

. It is found as needle-like or prismatic crystals in pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

. It was named after British Politician and mineral collector Robert Ferguson of Raith
Robert Ferguson of Raith
Robert Ferguson of Raith, was at various times a Whig Member of Parliament for Fifeshire, Haddingtonshire and Kirkcaldy Burghs, and at the time of his death he was Lord Lieutenant of the county of Fife.-Biography:...

(1767–1840)
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