Page 9 - The Science of Glass
P. 9

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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