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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. 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, 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.
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|Mineralogy Database Dictionary||Download this dictionary|
(Molecular Weight = 598.63 gm)
Calcium 2.01 % Ca
Cerium 14.04 % Ce
Yttrium 17.82 % Y
Aluminum 10.14 % Al
Iron 7.00 % Fe
Silicon 14.07 % Si
Hydrogen 0.17 % H
Oxygen 34.74 % O
Approved IMA 1987
Named after the Scottish mineralogist, T. Allan (1777-1833).
 Imperfect,  Imperfect
brown or black.
3.3 - 4.2, Average = 3.75
Translucent to opaque
Massive - Granular - Common texture observed in granite and other igneous rock., Disseminated - Occurs in small, distinct particles dispersed in matrix.,
5.5 - Knife Blade
Vitreous - Greasy
| Allanite-(Y) in Italian | Allanite-(Y) in Dutch | Allanite-(Y) in German | Allanite-(Y) in Polish | Allanite-(Y) in Latvian
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