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Fergusonite

Fergusonite is a mineral comprising a complex oxide of various rare-earth elements. The general chemical formula of fergusonite is NbO₄, where REE = rare-earth elements in solid solution with Y. Yttrium is usually dominant, but sometimes Ce or Nd... Wikipedia
Color: Black, black, brown, gray, yellow
Crystal class: Dipyramidal (4/m); H-M symbol: (4/m)
Crystal habit: Metamict – mineral originally crystalline, now amorphous due to radiation damage
Crystal system: Tetragonal
Formula mass: 245.81 g/mol (Y)
Formula (repeating unit): REENbO4 (REE: rare-earth element)
Mohs scale hardness: 5.5–6