Chapter 5 Summary

The topics covered in this chapter can be summarized as follows:

5.1 Atoms

An atom is made up of protons and neutrons in the nucleus, and electrons arranged in energy shells around the nucleus. The first shell holds two electrons, and outer shells hold more. Atoms strive to have eight electrons in their outermost shell (or two for H and He). Atoms gain, lose, or share electrons to achieve this. In so doing they become either positively charged cations (if they lose electrons) or negatively charged anions (if they gain them).

5.2 Bonding and Lattices

The main types of bonding in minerals are ionic bonding (electrons transferred) and covalent bonding (electrons shared). Some minerals have metallic bonding or weak Van der Waals forces. Minerals form in three-dimensional lattices. The configuration of the lattices and the type of bonding within help determine mineral properties.

5.3 Mineral Groups

Minerals are grouped according to the anion part of their formula. Some common types are: oxides, sulphides, sulphates, halides, carbonates, phosphates, silicates, and native minerals.

5.4 Silicate Minerals

Silicate minerals are the most common minerals in Earth’s crust and mantle. They all have silica tetrahedra (four oxygens surrounding a single silicon atom) arranged in different structures (chains, sheets, etc).

5.5 How Minerals Form

Most minerals in the crust form from the cooling and crystallization of magma. Some form from hot water solutions, during metamorphism or weathering, or through organic processes. More rarely, minerals precipitate directly from a gas, such as at a volcanic vent.

5.6 Mineral Properties

Some of the important properties for mineral identification include hardness, cleavage/fracture, density, lustre, colour, and streak colour.

Review Questions

1. What is the electrical charge of a proton? A neutron? An electron? What are their relative masses?

2. Explain how the need for an atom’s outer shell to be filled with electrons contributes to bonding.

3. Why are helium and neon non-reactive?

4. What is the difference in the role of electrons in an ionic bond compared to a covalent bond?

5. How do cations differ from anions?

6. What chemical feature is used in the classification of minerals into groups?

7. Name the mineral group for the following minerals:

8. What is the net charge on an unbonded silica tetrahedron?

9. What allows magnesium to substitute freely for iron in olivine?

10. How are the silica tetrahedra structured differently in pyroxene and amphibole?

11. Why is biotite called a ferromagnesian mineral, while muscovite is not?

12. What are the names and compositions of the two end-members of the plagioclase series?

13. Why does quartz have no additional cations (other than Si⁺⁴)?

14. Why is colour not necessarily a useful guide to mineral identification?

15. You have an unknown mineral that can scratch glass but cannot scratch a porcelain streak plate. What is its approximate hardness?