Sand and glass
How does sand become glass?
Glass is a transparent solid made by melting sand, silicon and oxygen born in stars, and cooling it before the atoms can arrange themselves into a crystal.
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In three stops
Where were its atoms born?
Silicon forms when oxygen burns in massive stars, and oxygen itself is a stellar product. The two combine into silica (SiO₂).
How did it form on Earth?
About 46% of Earth's crust by mass is oxygen and 28% is silicon; most rocks are silicates. As rocks like granite wear down, their tough quartz grains break free: that is most beach sand.
What did humans make of it?
Sand is melted with soda and lime at about 1,500 °C. When it cools quickly, the atoms have no time to form an orderly crystal, and a disordered, transparent solid results: glass. The first known glass objects were made in Mesopotamia about 4,500 years ago; glassblowing began about 2,000 years ago.
Did you know?
The chips in computers and phones are also built on extremely pure silicon made from sand.