Mineral Information and Data:

CaYFe2+Al2(Si2O7)(SiO4)O(OH) [CNMNC approved formula]

Named in 1949 and after the Scottish mineralogist, T. Allan (1777-1833) and the Y- content.

IMA status : Renamed IMA Approved; 1987 ()
(8th edition) :
58.02.01c.03  (This Dana# Changed)
  (58) Sorosilicate Insular, Mixed, Single, and Larger Tetrahedral Groups
  (58.02) with cations in [6] and higher coordination; single and double groups (n=1,2)
  (58.02.01c) Epidote group (Allanite subgroup)
(10th edition) :
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BG) Sorosilicates with mixed SiO4 and Si2O7 groups; cations in octahedral [6] and greater coordination
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 8.98 Å, b = 5.75, Å, c = 10.23 Å, b = 115°
Crystal Habit: Crystals tabular, long prismatic to acicular, commonly massive, bladed, or embedded grains.
Color: Black, dark brown
Diaphaneity: Opaque
Luster: Sub-Vitreous, Resinous, Waxy, Greasy; May be dull due to alteration
Hardness (Mohs): 5.5 - 6.5
Measured Density: 3.5 - 4.2 g/cm3
Cleavage: Imperfect on {001}; poor on {100} and {110}.
Tenacity: Very brittle
Fracture: Conchoidal to uneven
Streak: Light gray
Geologic Setting: An accessory in some granites and granite pegmatites, syenites, more rarely in gabbroic pegmatites. Rarely in schists, gneisses, and some contact metamorphosed limestones; a clastic component of sediments.
Mineral Association: Epidote, muscovite, fluorite
Comments: Dana Number Changed from 58.2.1a.3


Dark brown allanite-(Y)
Origin: Boden, Marienberg District, Erzgebirge, Saxony, Germany
Picture size: 10 mm
Photo and Owner: Thomas Witzke