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Hey there, can anyone help with this question:-Mineral amphibole is composed of double chains of SiO44− tetrahedra linked together by atoms of Ca, Fe and Mg. Atoms of Al can substitute for Si 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 amphibole differ from the chemical compositions of dark mica (biotite) and pyroxene?

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Have a look in your S104 coursebooks- all the answers are in there, I think you'll find!

To compare the chemical composition of amphibole with dark mica (biotite) and pyroxene, we can examine their respective mineral formulas:

1. Amphibole: Ca2(Mg,Fe)5Al2Si7O22(OH)2
2. Dark Mica (Biotite): K(Mg,Fe)3AlSi3O10(OH)2
3. Pyroxene: (Mg,Fe)SiO3

Here are the ways in which the chemical compositions of these minerals differ:

1. Elements present: Amphibole contains Ca, Mg, Fe, Al, and Si, while dark mica contains K, Mg, Fe, Al, and Si. Pyroxene only contains Mg, Fe, and Si.

2. Crystal structure: Amphibole is composed of double chains of SiO44− tetrahedra linked together by atoms of Ca, Fe, Mg, and Al. Dark mica has a sheet-like structure composed of interconnected SiO4, AlO6, and octahedral layers. Pyroxene has a single-chain structure of SiO44− tetrahedra linked together by atoms of Mg and Fe.

3. Substitution of elements: In amphibole, Al can substitute for Si, as well as Mg and Fe. In dark mica, Al can also substitute for Si. In pyroxene, there are no Al substitutions.

4. Hydroxyl group: Amphibole contains hydroxyl groups, represented by (OH)2, which are absent in both dark mica and pyroxene.

By analyzing the mineral formulas and understanding the chemical properties of the elements involved, we can identify the differences in the chemical compositions and structures of amphibole, dark mica (biotite), and pyroxene.