Fergusonite

Formula:  (Ce,La,Y)NbO4

Origin of name:   For R. Ferguson, Scottish physician

 

Crystal system:   Tetragonal

Crystal class:   Unknown

Twinning:

Unit cell: 

 

Colour:  Brownish black to black, crystal surfaces alter to gray, brown or yellow

Diaphaneity:  Opaque

Luster:   Vitreous, submetallic, dull

Habit:   Crystals short to long prismatic or pyramidal; massive, grains

Hardness:   5.5 to 6.5

Specific gravity:  5.70

Cleavage:   1; {111} trace

Tenacity: 

Streak:   Greenish grey, yellowish brown, brown

 

Synonyms/varieties:

 

Comments:  There are actually three closely related fergusonites (Ce, Nd, Y). Each one is dimorphic with the corresponding fergusonite-beta

 

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