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Allanite-(Y)

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Allanite
Allanite (also called orthite) 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, ceriumlanthanum or yttrium.

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Mineralogy Database Dictionary

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Allanite-(Y)

General Information:
 Chemical Formula:
(Y,Ce,Ca)2(Al,Fe+++)3(SiO4)3(OH)
 Composition:
(Molecular Weight = 598.63 gm)
Calcium 2.01 % Ca
Cerium 14.04 % Ce
Yttrium 17.82 % 
Aluminum 10.14 % Al
Iron 7.00 % Fe
Silicon 14.07 % Si
Hydrogen 0.17 % 
Oxygen 34.74 % 
 Empirical Formula:
Y1.2Ce0.6Ca0.3Al2.25Fe3+0.75(SiO4)3(OH)
 IMA Status:
Approved IMA 1987
 Name Origin:
Named after the Scottish mineralogist, T. Allan (1777-1833).
Physical Properties:
 Cleavage:
[001] Imperfect, [100] Imperfect
 Color:
brown or black.
 Density:
3.3 - 4.2, Average = 3.75
 Diaphaniety:
Translucent to opaque
 Habits:
Massive - Granular - Common texture observed in granite and other igneous rock., Disseminated - Occurs in small, distinct particles dispersed in matrix.,
 Hardness:
5.5 - Knife Blade
 Luminescence:
None.
 Luster:
Vitreous - Greasy
 Streak:
grayish brown
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