Crystals
Look closely at some table salt
through a magnifying glass. You’ll see that the bits of salt are made up of tiny
cubes. Each cube is a salt crystal. The salt crystals within the particles can
be different sizes, but they always have this shape.
TINY PARTICLES IN PATTERNS
A crystal contains identical
particles that are arranged in a particular pattern such as a cube, rectangle,
or hexagon. As a crystal grows in size, this pattern is repeated over and
over.
Salt is made up of the elements
sodium and chlorine. Extremely tiny particles of sodium and chlorine, called
atoms, form a repeating cubic pattern in a crystal of table salt. The more times
the pattern is repeated, the bigger the crystal that forms.
HOW DO CRYSTALS FORM?
Crystals form when some liquids
turn into solids. A liquid may freeze into a crystal. Snow, for example, is made
of tiny crystals of frozen water. Crystals can also be left behind when a liquid
dries out. When seawater in a rock pool dries out, tiny crystals of salt
remain.
Most of the rocks and minerals in
Earth’s crust are crystals. Some crystals were formed from melted rock when it
cooled and became solid. Others were left behind by the waters of a sea, lake,
or river that dried up long ago.
HOW DO WE USE CRYSTALS?
Many crystals are beautiful.
Diamonds, rubies, and emeralds are crystals that are made into attractive
jewelry. Crystals also have many practical uses. Quartz crystals are used in
clocks, radios, and sonar, the system that allows ships and submarines to see
things underwater. Quartz crystals can also be pressed or heated to make
electricity.
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