Allanite


Allanite
Allanite

Allanite from the Mt. Isa – Cloncurry area, Queensland, Australia (scale bar 1 inch)
General
Category Silicate mineral
Chemical formula (Ce,Ca,Y,La)2(Al,Fe+3)3(SiO4)3(OH)
Crystal symmetry Monoclinic 2/m
Unit cell a = 8.927 Å, b = 5.761 Å, c = 10.15 Å; β = 114.77°; Z = 2
Identification
Color Brown to black
Crystal habit Crystals tabular, prismatic to acicular; granular, massive; commonly metamict
Crystal system Monoclinic
Twinning Polysynthetic, common on {100}
Cleavage Imperfect to poor
Fracture Conchoidal to uneven
Tenacity Brittle
Mohs scale hardness 5.5–6
Luster Vitreous, resinous to submetallic
Streak Grey
Diaphaneity Translucent to opaque
Specific gravity 3.5 – 4.2
Optical properties Biaxial (-)
Refractive index nα = 1.715–1.791, nβ = 1.718–1.815, nγ = 1.733–1.822
Birefringence δ = 0.018–0.031
Pleochroism X = pale olive-green, reddish brown;
Y = dark brown, brownish yellow;
Z = dark reddish brown, greenish brown
2V angle Measured: 40° to 80°
Dispersion r > v; strong
Other characteristics May be radioactive
References [1][2][3]

Allanite is a sorosilicate group of minerals within the broader epidote group that contain a significant amount of rare earth elements. The mineral occurs mainly in metamorphosed clay rich sediments and felsic igneous rocks. It has the general formula A2M3Si3O12[OH] where the A sites can contain large cations such as Ca2+, Sr2+, and rare earth elements and the M sites admit Al3+, Fe3+, Mn3+, Fe2+, or Mg2+ among others[4]. However, a large amount of additional elements, including Th, U, Zr, P, Ba, Cr and others may be present in the mineral. The International Mineralogical Association lists three minerals in the allanite group, each recognized as a unique mineral: allanite-(Ce), allanite-(La) and allanite-(Y), depending on the dominant rare earth present, cerium, lanthanum or yttrium.

Allanite crystals on smokey quartz from the White Mountain Wilderness, Lincoln County, New Mexico, USA (size: 2.7×1.8×1.7 cm)

Allanite, also called orthite, contains up to 20% rare earth elements and is a valuable source of them. The inclusion of thorium and other radioactive elements in allanite results in some interesting phenomena. Allanite often has a pleochroic halo of radiation damage in the minerals immediately adjacent. Also highly radioactive grains of allanite often have their structure disrupted or are metamict. The age of allanite grains that have not been destroyed by radiation can be determined using different techniques.[5]

Allanite is usually black in color, but can be brown, brown-violet. It is often coated with a yellow-brown alertation product,[6] likely limonite. It crystallizes in the monoclinic system and forms prismatic crystals. It has a Mohs hardness of 5.5–6 and a specific gravity of 3.5–4.2. It is also pyrognomic, meaning that it becomes incandescent at a relatively low temperature of about 95 °C.

It was discovered in 1810 and named for the Scottish mineralogist, Thomas Allan (1777–1833).[1] The type locality is Aluk Island, Greenland[2] where it was first discovered by Karl Ludwig Giesecke.

References

  1. ^ a b Allanite-(Ce). Handbook of Mineralogy
  2. ^ a b Allanite. Mindat.org
  3. ^ Allanite. Webmineral
  4. ^ Dollase, W.A. (1971). "Refinement of the crystal structure of epidote, allanite, and hancockite". American Mineralogist, 56: 447–464. http://rruff.info/uploads/AM56_447.pdf. 
  5. ^ Catlos, E.J., Sorensen, S.S., Harrison, T.M. (2000). "Th-Pb ion-microprobe dating of allanite". American Mineralogist 85: 633–648. http://sims.ess.ucla.edu/PDF/catlos_et_al_AMMIN_2000.pdf. 
  6. ^ Klein, C., Dutrow, B. (2007) Manual of Mineral Science. Wiley Publishers, p. 500

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Look at other dictionaries:

  • allanite — ● allanite nom féminin (de T. Allan, nom propre) Silicate naturel de la famille des épidotes, contenant des terres rares (cérium, lanthane, néodyme, praséodyme). ● allanite (synonymes) nom féminin (de T. Allan, nom propre) Silicate naturel de la… …   Encyclopédie Universelle

  • Allanite — Al lan*ite, n. [From T. Allan, who first distinguished it as a species.] (min.) A silicate containing a large amount of cerium. It is usually black in color, opaque, and is related to epidote in form and composition. [1913 Webster] …   The Collaborative International Dictionary of English

  • allanite — alanitas statusas T sritis chemija apibrėžtis Mineralas. formulė (Ca,Ce,Th)(Fe,Mg)Al₂[O|OH|SiO₄|Si₂O₇] atitikmenys: angl. allanite; ortite rus. алланит; ортит ryšiai: sinonimas – ortitas …   Chemijos terminų aiškinamasis žodynas

  • allanite — allanitic /al euh nit ik/, adj. /al euh nuyt /, n. Mineral. a member of the epidote group, a silicate of calcium, cerium, aluminum, and iron, occurring chiefly in brown to black masses or prismatic crystals. [1835 45; named after Thomas Allan… …   Universalium

  • allanite — noun Any of a group of silicate minerals that are a source of rare earth metals …   Wiktionary

  • allanite — [ alənʌɪt] noun a brownish black mineral of the epidote group, consisting of a silicate of rare earth metals, aluminium, and iron. Origin C19: named after the Scottish mineralogist Thomas Allan + ite1 …   English new terms dictionary

  • allanite — al·lan·ite …   English syllables

  • allanite — /ˈælənaɪt/ (say aluhnuyt) noun a mineral, a silicate of calcium, cerium, aluminium, and iron, chiefly occurring in brown to black masses or prismatic crystals; orthite. {named after Thomas Allan, 1777–1833, English mineralogist. See ite1} …   Australian English dictionary

  • allanite — …   Useful english dictionary

  • List of minerals A-B (complete) — It is currently not possible to have a complete list of minerals . The International Mineralogical Association is the international group that recognises new minerals and new mineral names, however minerals discovered before 1959 did not go… …   Wikipedia