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Mineralogical Society of America

Figure 1.6

Would you expect the space inside an 8-coordinated site to be smaller or larger than 4- or 6-coordination?

smaller

larger

The amount of space inside a tetrahedron of four oxygens is significantly smaller than the space inside an octahedron of six oxygens. This difference governs the size of the cation that can fit in the sites. Small, highly-charged cations like Si⁴⁺ and AI³⁺ like the tetrahedral site, while larger cations such as Fe²⁺ and Mg²⁺ prefer the octahedral, 6-coordinated site.

Figure 1.1

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Figure 1.3

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Figure 1.5

Figure 1.7

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