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| Named in 1810 by Thomas Thomson for Thomas Allan (1777-1833), Scottish
mineralogist, who first observed the mineral.
| Discovered
in 1810;
IMA
status: Valid (pre-IMA; Grandfathered) |
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Chemistry
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Chemical
Formula: |
(Ca;Ce)2(Al;Fe2+;Fe3+)3(SiO4)(Si2O7)O(OH)
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Calcium
Cerium Yttrium Aluminum Iron Silicate Hydroxide |
Molecular
Weight: |
614.71 gm |
Composition: |
Calcium |
3.91 % |
Ca |
5.47 % |
CaO |
|
Cerium |
27.35 % |
Ce |
32.04 % |
Ce2O3 |
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Yttrium |
4.34 % |
Y |
5.51 % |
Y2O3 |
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Aluminum |
9.88 % |
Al |
18.66 % |
Al2O3 |
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Iron |
6.81 % |
Fe |
9.74 % |
Fe2O3 |
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Silicon |
13.71 % |
Si |
29.32 % |
SiO2 |
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Hydrogen |
0.16 % |
H |
1.47 % |
H2O |
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Oxygen |
33.84 % |
O |
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100.00 % |
|
100.00 % |
= TOTAL OXIDE |
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Classification
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Mineral
Classification: |
Silicates
(Germanates)
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Strunz 8th
Ed. ID:
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8/C.23-80
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Nickel-Strunz 10th
Ed. ID:
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9.BG.05
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9 : SILICATES (Germanates)
B : Sorosilicates G :
Sorosilicates with mixed SiO4 and Si2O7 groups;
cations in octahedral [6] and greater coordination
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Related
to: |
Epidote
Group
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Members
of Group: |
Epidote
Group: Allanite, Askagenite, Clinozoisite, Dissakisite,
Dollaseite, Epidote, Ferriallanite, Khristovite,
Manganiandrosite, Manganipiemontite, Mukhinite, Piemontite,
Uedaite, Vanadoandrosite, Zoisite
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Varieties: |
Chromian Allanite-(Ce),
Allanite-(Ce), Allanite-(La), Allanite-(Y)
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Synonyms: |
Cerepidote,
Cerine, Cerorthite
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Crystal
Data
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Crystallography:
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Monoclinic
- Prismatic
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Crystal
Habit:
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Crystals
tabular, or prismatic to acicular, to 90 cm; granular,
massive.
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Twinning:
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Polysynthetic,
common on [100]
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Physical
Properties
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Cleavage: |
Imperfect
on [001], Poor on [100], Poor on [110]
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Fracture: |
Irregular/Uneven,
Conchoidal
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Tenacity:
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Brittle
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Moh's
Hardness: |
5.5 - 6.0
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Density:
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3.50
- 4.20 (g/cm3)
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Luminescence:
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None
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Radioactivity:
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Weak;
GRapi = 27,438.55 (Gamma Ray American Petroleum Institute Units)
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Optical
Properties
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Color: |
Black,
dark Brown, dark Reddish Brown, dark Greenish Brown
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Transparency: |
Translucent
to Opaque |
Luster: |
Vitreous,
Resinous to Sub-Metallic |
Refractive
Index: |
1.715
- 1.822 Biaxial ( - ); Metamict Allanites are isotropic with N as low as 1.61
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Birefringence: |
0.018 - 0.031
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Dispersion: |
Distinct
to Strong; r > v |
Pleochroism: |
X
= pale olive-green, reddish brown; Y = dark brown,
brownish yellow; Z = dark reddish brown, greenish
brown
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Occurances
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Geological
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. |
Common
Associations: |
Epidote,
Fluorite, Muscovite |
Common
Impurities: |
None
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Type
Locality: |
Aluk Island, Prins Christian Sound, Kitaa (West
Greenland) Province, Greenland |
Year
Discovered: |
1810
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View
mineral photos: |
Allanite
Mineral Photos and Locations |
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More
Information
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Mindat.org
Webmineral.com
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Allanite-(Ce)
is
a rare member of the Epidote Group of minerals that
includes Allanite, Clinozoisite, Epidote,
Hancockite, Mukhinite,
Piedmontite, Tanzanite,
Thulite
and Zoisite. Allanite
is very rarely faceted and is usually metamict due to
the presence of Cerium (Ce) in its chemical composition.
Metamict is the break down of the internal crystal structure
by rare earth and radioactive elements. Allanite is
usually opaque black but may also be found as light
to dark brown or greenish brown crystals. The black,
opaque crystals are usually larger and the transparent
brownish crystals are usually too small for faceting.
Allanite is found in many locations worldwide.
Widespread;
some localities affording good crystals or rich material
follow. From Qáqarssuatsiaq, Alluk, south Greenland.
At Ytterby and Finbo, Sweden. From Kragerö, Arendal,
and on Hitterö Island, Flekkefjord, Norway. From Sillböle,
Stansvik, and Vaarala, Finland. At Miass, Ilmen Mountains,
Southern Ural Mountains, Russia. From the Trimouns talc
deposit, six km northeast of Luzenac, Ariμege, France.
In the USA, at Pacoima Canyon, Los Angeles County, California;
in the Baringer Hill pegmatite, 26 km west of Burnet,
and on the Rode Ranch, Llano County, Texas. In Canada,
from Olden Township, Frontenac County, Quebec; in the
McDonald mine, Hybla, Ontario; and at Hoidas Lake, near
Nisikkatch Lake, Saskatchewan. From near Telixtlahuaca,
Oaxaca, Mexico. In the Mary Kathleen mine, Queensland,
and at Broken Hill, New South Wales, Australia. From
Ribuae, Mozambique.
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