Minerals

We live in a world of minerals—they are everywhere around us. Gems and jewelry are

minerals. Gravel and sand are minerals. Mud is a mixture of microscopic minerals. Ice is a

mineral, and even dust in the air we breathe is made up of tiny mineral grains. Minerals

sustain our lives and provide continuously for society.The houses in which we live, the automobiles

we drive, as well as the roads and other structures of our society, and almost

everything we touch are made of minerals or material derived from minerals. Indeed, on

average, every person on Earth uses, directly or indirectly, 10 metric tons of minerals each

year.

But the importance of minerals extends far beyond their value as economic deposits.

Minerals are also the substance of Earth’s natural systems.The green and white crystals in

this beautiful photograph are two very different minerals.The lustrous pastel green crystals

are apophyllite and the sparkling white needles are mesolite. Each mineral has distinguishing

properties. Every one of the tiny ice-clear crystals in these radial sprays of mesolite has

much in common with all of the other grains of its mineral species. For example, all grains

of mesolite have the same internal arrangement of atoms and have the same chemical and

physical properties even though individuals may vary greatly in size and shape.The atomicstructure of mesolite creates a natural chemical sieve. Its open structure allows some molecules

and ions dissolved in water to move through the framework of the atoms, but it will

filter out the larger molecules. Mesolite’s internal structure contains chains of atomic tetrahedrons

aligned in one direction; this produces the needle-like shape of the crystals.The

mineral breaks preferentially between the long chains where atomic bonds are weakest.

All of Earth’s dynamic processes involve the growth and destruction of minerals as

matter changes from one state to another. As Earth’s surface weathers and erodes, some

minerals are destroyed and others grow in their place. Mesolite and apophyllite in this photo

grew from a watery solution as flowed through ancient lava flows. As sediments accumulate

in the oceans, minerals also grow from solution. Other minerals grow from molten rock when

lava erupts from volcanoes and cools. Deep below Earth’s surface, high pressure and temperature

remove atoms from the crystal structures of some minerals and cause them to recombine

them into new minerals. As tectonic plates move and continents drift, minerals are created

and destroyed by a variety of processes. Some knowledge of Earth’s major minerals,

therefore, is essential to understanding Earth’s dynamics.

In this chapter, we survey the general characteristics of minerals and the physical properties

that identify them.We then explore the major rock-forming minerals in preparation

for a study of the major rock types in Chapters 4, 5, and 6.