The Earth -- Introduction

Class Notes - Minerals

States of Matter

Structure of an Atom

Chemical Bonding

The Chemical Composition of the Continental Crust

Mineral Structures

In the definition of a mineral it was noted that a mineral has a fixed composition (like quartz) or a composition that is variable within a limit. Consider the two minerals Forsterite and Fayalite.

Note that the two minerals differ chemically in that one has Mg (magnesium) and the other Fe (iron). The rest of the chemical formulas are identical. Note that both Mg and Fe sit in 6 fold sites (octahedral). The sizes of these two ions are nearly identical, the charge on both is +2 and the Mg-O and Fe-O bonds are dominately ionic in nature. When such similarities occur the ions may substitute for each other forming a solid solution series. The series between these two end members is called the olivine series. Compositions range from pure Forsterite to pure Fayalite. Not all solid solution series are complete; some exhibit a limited amount of substitution.

Almost all of the common minerals we will work with are solid solution series. Quartz is the notable exception.

Classification of Minerals



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Copyright by John C. Butler, July 29, 1995