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 % Y
Aluminum 10.14 % Al
Iron 7.00 % Fe
Silicon 14.07 % Si
Hydrogen 0.17 % H
Oxygen 34.74 % O
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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