Page 9 - The Science of Glass
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The Origins of Glass
Although the glass we use today is man-made, the earliest example
of glass on Earth occurs naturally. It is called obsidian. Obsidian
forms when volcanoes erupt. Molten rock in the form of lava pours
out. When lava cools quickly, it sometimes hardens as this smooth
glass. It is usually black or green. It is also translucent.
Obsidian can be found in rock formations around the world. There
is a large amount of the shiny glass on the Obsidian Cliff in Wyoming.
People can pick up chunks of it at the base of the tall, black cliff.
Throughout history, people have used obsidian for many purposes.
American Indians used it to make weapons, such as knives and
arrows. It was easily broken into shapes for blades or arrowheads.
People in ancient Greece used obsidian for mirrors.
Obsidian has many modern uses too. Some medical instruments,
such as scalpels, can be made of obsidian. They are even sharper
than steel. Jewelry made from obsidian is popular too. Some people
believe the glass has healing properties. They also think that obsidian
brings good luck to a person who wears it!
Science
Molten Glass
Glass is made by melting together several
minerals. The main ingredient is usually
silica. Silica often comes in the form of sand.
The minerals are mixed together and melted
in a furnace. Temperatures can go as high
as 1,700° Celsius (3,100° Fahrenheit). The
solids liquefy and form molten glass. The
malleable molten glass is removed from the
furnace. Then, it is shaped and allowed to cool
and harden.
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