Allanite

Formula: (Ce,Ca,Y)2(Al,Fe,Fe,)3(SiO4)3(OH)

Origin of name:  For Thomas Allan (1777-1833), Scottish mineralogist who discovered this mineral

 

Crystal system:  Monoclinic

Crystal class:  2/m

Twinning:  Common on {100}, polysynthetic

Unit cell:  a = 8.93 Å, b = 5.77 Å, c = 10.16 Å, b = 114.7°

 

Colour:  Brown to black

Diaphaneity: Translucent to opaque

Luster:  Resinous or submetallic

Habit:  Crystals tabular, long prismatic to acicular, commonly massive, bladed, or embedded grains.

Hardness:  5.5 to 6

Specific gravity:  4.12

Cleavage:  None

Tenacity:  Brittle

Streak:  Gray

 

Synonyms/varieties:  Orthite, yttrorthite [allanite-(Y)]

 

Comments:  Three distinct species with the extensions -(Ce), -(La) and -(Y) indicating the predominant rare earth cation in the formula. Member of the epidote group. Accessory mineral in some granites and granite pegmatites, more rarely in gabbroic pegmatites. Rarely found in schists, gneisses and some contact metamorphosed limestones, a clastic component of sediments.

 

Back to Alphabetical list Colour photos: Allanite-(Ce), Allanite-(Y) Optical properties/Thin sections SEM images TEM images vibrational spectra description IR spectra Raman spectra N-IR spectra F-IR spectra IES spectra