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Allanite-(Ce)

Discovered in 1810; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Ca;Ce)₂(Al;Fe²⁺;Fe³⁺)₃(SiO₄)(Si₂O₇)O(OH)

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

Yttrium

4.34 %

Y

5.51 %

Y₂O₃

Aluminum

9.88 %

Al

18.66 %

Al₂O₃

Iron

6.81 %

Fe

9.74 %

Fe₂O₃

Silicon

13.71 %

Si

29.32 %

SiO₂

Hydrogen

0.16 %

H

1.47 %

H₂O

Oxygen

33.84 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/C.23-80

Nickel-Strunz 10th Ed. ID:

9.BG.05

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO₄ and Si₂O₇ groups; cations in octahedral [6] and greater coordination

Related to:

Epidote Group

Members of Group:

Epidote Group: Allanite, Askagenite, Clinozoisite, Dissakisite,  Dollaseite, Epidote, Ferriallanite, Khristovite, Manganiandrosite, Manganipiemontite, Mukhinite, Piemontite, Uedaite, Vanadoandrosite, Zoisite

Varieties:

Chromian Allanite-(Ce), Allanite-(Ce), Allanite-(La), Allanite-(Y)

Synonyms:

Cerepidote, Cerine, Cerorthite

Crystal Data

Crystallography:

Monoclinic - Prismatic (may be metamict - a mineral originally crystalline, eventually amorphous due to radiation damage)

Crystal Habit:

Crystals tabular, or prismatic to acicular, to 90 cm; granular, massive.

Twinning:

Polysynthetic, common on [100]

Physical Properties

Cleavage:

Imperfect on [001], Poor on [100], Poor on [110]

Fracture:

Irregular/Uneven, Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.5 - 6.0

Density:

3.50 - 4.20 (g/cm³)

Luminescence:

None

Radioactivity:

Weak; GRapi = 27,438.55 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Black, dark Brown, dark Reddish Brown, dark Greenish Brown

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

Birefringence:

0.018 - 0.031

Dispersion:

Distinct to Strong; r > v

Pleochroism:

X = pale olive-green, reddish brown; Y = dark brown, brownish yellow; Z = dark reddish brown, greenish brown

Occurances

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

Type Locality:

Aluk Island, Prins Christian Sound, Kitaa (West Greenland) Province, Greenland

Year Discovered:

1810

View mineral photos:

Allanite Mineral Photos and Locations

Unusual Gem Categories

Metamict Gems, Radioactive Gems 

More Information

Mindat.org
Webmineral.com

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 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.

Because Allanite is a weakly radioactive mineral it should be stored away from other gems and minerals that are subject to damage from radioactivity and of course human exposure should be limited.

Allanite is usually metamict due to the presence of radioactive Cerium (Ce) in its chemical composition. Metamictization is a natural, gradual process of destruction of the internal crystal structure of a mineral due to radiation present in the mineral or from nearby external radiation. Metamictization eventually leaves the mineral amorphous or without any internal crystal structure. Once this process is complete the mineral is described as metamict.

Allanite was named in 1810 by British chemist and mineralogist Thomas Thomson (1773-1852) to honor Scottish mineralogist Thomas Allan (1777-1833), who first observed the mineral.

Allanite is found at many locations worldwide. Some locations for good crystals 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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