Читать книгу Geology For Dummies - Alecia M. Spooner - Страница 84

The bonding of elements to form compounds is fundamental to understanding the formation of rocks and minerals (which I describe in Chapter 6). When scientists discuss the processes of rock formation, as well as other earth processes involving chemical changes (such as weathering, described in Chapter 7), they use a shorthand of chemical formulas.

The chemical formula of a compound describes the number of different atoms of each element that are combined into a compound. For example, the chemical formula for quartz is as follows:

SiO₂

This formula indicates that one atom of silicon (Si) and two atoms of oxygen (O) have bonded together, forming the compound.

In the case of geology, most chemical formulas describe minerals, which are solid structures built of molecules (see Chapter 6). In mineral compounds, sometimes multiple elements can fill the same spot in the mineral structure. For example, the mineral olivine has this formula:

(Mg, Fe)₂SiO₄

Two atoms of either magnesium (Mg) or iron (Fe) will combine with one atom of silicon (Si) and four atoms of oxygen (O). Either magnesium or iron can create the mineral olivine, so when you write the chemical formula, you put a parenthesis around and a comma separating the possible atoms that can form that particular chemical compound.