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Kamis, 12 Juli 2012


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.

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