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    Please could nybody help with this question as I am very helpless...tried to think for two days but cannot do no more...

    The mineral AMPHIBOLE is composed of double chains of SiO4 tetrahedra linked together by atoms of Ca, Fe and Mg. Atoms of Al can substitute for Si (as in feldspar) and can also substitute for Mg and Fe. An example of the mineral formula of amphibole from an igneous rock is
    Ca2(Mg,Fe)5Al2Si7O22(OH)2
    in what ways does the chemical composition of the igneous amphibole differ from the chemical composition of ( i ) dark mica (biotite) and (ii ) pyroxene?
    Note: you do not need to consider the proportions of the various elements in these minerals
    How do these differences account for the observation that amphibole tends to crystallise at lower temperatures than pyroxene, but higher temperature than mica?
 
 
 
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